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Example 5.1: A C program to display a pattern.
Answer:
#include <stdio.h>
int main()
{
int k, i;
for (k = 1; k <= 5; k++)
{
for ( i = 1; i <= (6-k); i++)
{
printf("X ");
}
printf("\n");
}
return 0;
}
MEANING:
The provided C code
prints a right-angled triangle pattern of 'X' characters to the console. The
output will look like this:
X X X X X
X X X X
X X X
X X
X
Code Explanation:
·
#include <stdio.h>: This line includes the standard input/output library, which
provides functions like printf for displaying
output.
·
int main() { ... }: This is the main function where the program execution begins.
·
for (k = 1; k <= 5; k++) { ... }: This outer loop controls the number of rows
printed. It iterates 5 times (for k=1, 2, 3, 4, 5).
·
for ( i = 1; i <= (6-k); i++) { ... }: This inner loop controls the number of 'X'
characters printed in each row.
o The expression (6-k) determines the number of 'X's.
o For the first row (k=1), it prints 5 'X's.
o For the second row (k=2), it prints 4 'X's,
and so on.
·
printf("X ");: Prints the character 'X' followed by a space during the inner
loop.
·
printf("\n");: After the inner loop finishes (a row is complete), this
statement prints a newline character, moving the cursor to the beginning of the
next line for the next row.
·
return 0;:
Indicates that the program executed successfully.
Example 5.2: A C program to display a dynamic pattern.
Answer:
#include <stdio.h>
int main()
{
int k, i, N;
printf("Please enter number of lines to be displayed:
");
scanf("%d", &N);
for (k = 1; k <= N+1; k++)
{
for ( i = 1; i <= (N+1-k); i++)
{
printf("X ");
}
printf("\n");
}
return 0;
}
Meaning:
This C program is
designed to print a right-angled triangle pattern of 'X'
characters that decreases in size as it moves downward.
Here is a breakdown of
how the logic works and what the output looks like.
Code Logic Breakdown
The program uses nested loops to control the rows and columns of the
output:
1.
Outer
Loop (k): This loop keeps track of the current row. It starts at 1 and
runs until it reaches $N+1$.
2.
Inner
Loop (i): This loop determines how many "X " characters to
print on the current line.
o The condition i <= (N + 1 - k) ensures that as $k$ (the row number) increases, the number of
'X's decreases.
3.
New
Line (\n): After the inner loop finishes printing characters for a row,
this moves the cursor to the next line.
Example Execution
If you enter 5 when prompted, the program will calculate the rows as
follows:
·
Row
1 (k=1):
Prints 5 + 1 - 1 = 5 times.
·
Row
2 (k=2):
Prints 5 + 1 - 2 = 4 times.
·
...and so on.
Output for N = 5:
Plaintext
X X X X X
X X X X
X X X
X X
X
(Note: Because the outer loop
goes up to N+1, the last iteration where k = 6 results in $6-6=0$ characters, effectively ending the pattern.)
Observations & Tips
·
The
$N+1$ Logic:
Your code actually prints $N$ lines of content. If you enter 5, you get a 5-row
triangle. The extra +1 in the loop conditions is what allows the
"countdown" effect to reach 1 before stopping.
·
Formatting: The space after the X in printf("X "); makes the output look like a grid. If you remove it, the 'X's
will be bunched together.
Would you like me to
show you how to modify this code to flip the triangle so it starts small and
grows larger?
Example 5.3: A C program to display a pattern.
Answer:
#include <stdio.h>
int main()
{
int k, i;
// decreasing portion
for (k = 1; k <= 5; k++)
{
for ( i = 1; i <= (6-k); i++)
{
printf("X ");
}
printf("\n");
}
// increasing portion
for (k = 1; k <= 4; k++)
{
for ( i = 1; i <= k+1; i++)
{
printf("X ");
}
printf("\n");
}
return 0;
}
Meaning:
This code combines two
separate nested loop structures to create a sideways hourglass
or a left-aligned "V" shape (pointing right).
By hardcoding the
values (using 5, 6, and 4), you have created a fixed-size pattern that
first shrinks and then grows.
The Resulting Pattern
When you run this
code, it produces the following output:
Plaintext
X X X X X <-- k=1 (6-1 = 5)
X X X X <-- k=2 (6-2 = 4)
X X X <-- k=3 (6-3 = 3)
X X <-- k=4 (6-4 = 2)
X <-- k=5 (6-5 = 1)
X X <-- k=1 (1+1 = 2)
X X X <-- k=2 (2+1 = 3)
X X X X <-- k=3 (3+1 = 4)
X X X X X <-- k=4 (4+1 = 5)
How the Logic Shifts
The code is split into
two distinct logical blocks:
1. The Decreasing Portion
·
The outer loop runs 5 times.
·
The inner loop uses
the formula $(6 - k)$.
·
As $k$ increases, the
number of 'X's decreases from 5 down to 1.
2. The Increasing Portion
·
The outer loop runs 4 times.
·
The inner loop uses
the formula $(k + 1)$.
·
It starts at $k=1$, so
the first line of this section prints 2 'X' characters
(ensuring it doesn't repeat the single 'X' from the previous section). It
finishes by printing 5 'X's.
A Quick Tip for Flexibility
If you want to be able
to change the size of the entire shape easily, you can use a variable N for the maximum width
instead of hardcoded numbers:
C
int N = 5;
// Decreasing
for (k = 0; k < N; k++) {
for (i = 0; i < (N - k); i++) printf("X ");
printf("\n");
}
// Increasing (starts
from 2 to avoid repeating the single X)
for (k = 2; k <= N; k++) {
for (i = 0; i < k; i++) printf("X ");
printf("\n");
}
Example 5.4: A C program to display a pattern.
Information:
The pseudo-code for this can be written as follows.
for k = 1 to 5
Display SPACE (5-k) times
Display X, k times
Go to the next line
Example 5.4 shows the complete C program for displaying the pattern. We used
the variable
“i” for displaying the space and the variable “j” for displaying
the character X. We can see that there is one outer loop in the program and
there are two inner loops.
Answer:
#include <stdio.h>
int main()
{
int i, j, k;
for (k = 1; k<=5; k++)
{
for(i = 1; i<=(5-k); i++)
{
printf(" ");
}
for(j = 1; j<= k; j++)
{
printf("X");
}
printf("\n");
}
return 0;
}
Meaning:
This code introduces a
third loop variable, i, to handle leading spaces. This
shifts the triangle from the left side of the screen to the right side,
creating a right-aligned triangle.
How the Logic Works
By printing spaces before the 'X' characters on the same line, you push
the 'X's to the right.
1.
Outer
Loop (k): Controls the rows (1 to 5).
2.
First
Inner Loop (i): Prints spaces. The number of spaces is $(5 - k)$.
o Row 1: 4 spaces
o Row 2: 3 spaces... and so on.
3.
Second
Inner Loop (j): Prints the 'X' characters. The number of 'X's is equal to the
row number $k$.
The Output
Plaintext
X
XX
XXX
XXXX
XXXXX
Key Difference: Left vs. Right Alignment
The addition of the
"space loop" is the standard way to handle alignment in CLI patterns.
Here is a quick comparison of the logic:
|
Alignment |
Logic Sequence |
|
Left-Aligned |
Print 'X' $\rightarrow$ Print Newline |
|
Right-Aligned |
Print Spaces $\rightarrow$ Print 'X' $\rightarrow$ Print Newline |
Helpful Tweak: The "Pyramid" Effect
If you want to turn
this right-aligned triangle into a centered Pyramid, you only
need to make one tiny change. If you add a space after the X in your second inner
loop:
C
printf("X "); // Adding a space here
The output would
instantly transform into this:
Plaintext
X
X X
X X X
X X X X
X X X X X
Example 5.5: A C program to display a pattern.
Some information:
Task 1 and Task 2 are for the left part and Task 3 is for the
right part. The pseudo-code for all the tasks can be written as follows.
for k = 1 to 5
Display SPACE (5-k) times.
Display X, k times.
Display X, (k-1) times.
Go to the next line.
Now the complete program is shown in Example 5.5. The first inner for
loop is responsible for performing Task 1 (line numbers 7 to 10). The second
inner for loop is responsible for performing Task 2 (line numbers 11 to 14).
The third inner for loop is responsible for performing Task 3 (line numbers 15
to 18).
Answer:
#include <stdio.h>
int main()
{
int i, j, k, p;
for (k = 1; k <=5; k++)
{
for(i = 1; i<=(5-k); i++)
{
printf(" ");
}
for(j = 1; j <= k; j++)
{
printf("X");
}
for(p = 1; p <= (k-1); p++)
{
printf("X");
}
printf("\n");
}
return 0;
}
MEANING:
This code creates a solid pyramid of 'X' characters.
By adding that third
inner loop (p), you have moved beyond a simple
right-aligned triangle to a symmetrical pyramid. Here is how the logic breaks
down:
How the Logic Works
The program builds
each row using three distinct steps:
1.
The
Space Loop (i): Prints leading spaces to center the pyramid.
2.
The
First 'X' Loop (j): Prints the left half of the pyramid (including the center
column).
3.
The
Second 'X' Loop (p): Prints the right half of the pyramid ($k-1$ characters).
The Output
For $k=1$ to $5$, the
output looks like this:
Plaintext
X (4 spaces, 1 X from j-loop, 0 X from
p-loop)
XXX (3 spaces, 2 X from j-loop, 1 X from
p-loop)
XXXXX (2 spaces, 3 X from j-loop, 2 X from
p-loop)
XXXXXXX (1 space,
4 X from j-loop, 3 X from p-loop)
XXXXXXXXX (0 spaces, 5
X from j-loop, 4 X from p-loop)
Key Observations
·
Odd
Numbers: Notice that the total
number of 'X's in each row follows the sequence of odd numbers: $1, 3, 5, 7,
9$. This is because the total 'X's per row equals $k + (k-1)$, which simplifies
to $2k - 1$.
·
Symmetry: Because the p loop always prints
one fewer 'X' than the j loop, the j loop provides the "center axis" of
the pyramid.
A Cleaner Alternative
You can actually
achieve this same result using only two loops instead of
three by changing the math in the second loop:
C
for (k = 1; k <= 5; k++) {
for (i = 1; i <= (5 - k); i++) printf(" ");
// Print (2*k - 1) characters in one go
for (j = 1; j <= (2 * k - 1); j++) printf("X");
printf("\n");
}
Example 5.6: A C
program to display a pattern.
Answer:
#include <stdio.h>
int main()
{
int i, j, k, p;
for (k = 1; k <=5; k++)
{
for(i = 1; i<=(5-k); i++)
{
printf(" ");
}
for(j = 1; j <= (2*k - 1); j++)
{
printf("X");
}
printf("\n");
}
return 0;
}
MEANING:
This version of the
code is more efficient! By combining the two "X" loops into a single
loop that prints (2*k - 1) characters, you are using the mathematical
property of odd numbers to create the pyramid.
How the Math Works
Each row $k$ now
calculates the exact number of 'X's needed to stay symmetrical:
·
Row
1 ($k=1$):
$2(1) - 1 = 1$ "X"
·
Row
2 ($k=2$):
$2(2) - 1 = 3$ "X"
·
Row
3 ($k=3$):
$2(3) - 1 = 5$ "X"
·
Row
4 ($k=4$):
$2(4) - 1 = 7$ "X"
·
Row
5 ($k=5$):
$2(5) - 1 = 9$ "X"
Comparison: Your Previous Code vs. This Code
Both programs produce
the exact same visual output, but the logic is slightly
different:
|
Feature |
Three-Loop Version |
Two-Loop (2k-1)
Version |
|
Logic |
Builds left half, then right
half. |
Calculates the full width of
the row. |
|
Readability |
Easier to see the
"mirror" effect. |
Mathematically cleaner and
more concise. |
|
Performance |
Slightly more overhead (extra
loop). |
Faster (fewer loop
initializations). |
The Output
Plaintext
X
XXX
XXXXX
XXXXXXX
XXXXXXXXX
Challenge: The Inverted Pyramid
If you wanted to flip
this pyramid upside down, you would just need to change how the outer loop $k$
counts. If you start $k$ at 5 and count down to 1, the math (5-k) for spaces and (2*k-1) for 'X's will
automatically reverse the shape.
Example 5.7: A C program
to display a pattern
Answer:
#include <stdio.h>
int main()
{
int i, j, k;
for (k = 1; k <=5; k++)
{
for(i = 1; i<=(5-k); i++)
{
printf(" ");
}
for(j = 1; j <= (2*k - 1); j++)
{
printf("%d ", j);
}
printf("\n");
}
return 0;
}
Meaning:
This version of the
code is an interesting variation! By changing printf("X") to printf("%d
", j), you have created a Number Pyramid where each row counts up from 1 to the
maximum width of that row.
The Math & Logic
1.
Leading
Spaces: Just like the
previous version, (5 - k) spaces are printed to center the numbers.
2.
The
Number Loop (j): This loop runs from 1 to (2*k
- 1).
3.
The
Output Format: Because you added a
space after the %d, the pyramid becomes wider and looks more
like a spread-out triangle.
The Output
For $k=1$ to $5$, the
code produces this:
Plaintext
1
1 2 3
1 2 3 4 5
1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9
A Logic "Gotcha" to Watch For
Because you added a
space after the number (%d ), the alignment might look a bit shifted
compared to your solid "X" pyramid. In the "X" version, one
character took one space. Here, the number plus a space takes
two spaces.
If you want the
pyramid to stay perfectly centered with the space after the number, you would
actually need to double the leading spaces in your i loop:
C
for(i = 1; i <= (5 - k) * 2; i++) // Doubling spaces to
match the "%d " format
The Palindrome Challenge
A very popular
interview variation of this is the Palindrome Pyramid,
where the numbers count up and then back down (e.g., 1 2 3 2 1).
To do that, you would
split your j loop back into two parts:
1.
A loop that counts up from 1 to k.
2.
A loop that counts down from k-1 to 1.
Exercise :
1. Write C programs to display the following patterns using nested loop construct.
(a)
1 2 3
1 2 3
1 2 3
1 2 3
1 2 3
Answer:
To display this
pattern, you need a grid where every row is identical. This is the most
fundamental use of a nested loop: the outer loop creates
the rows, and the inner loop handles the sequence of numbers within each row.
The Logic
1.
Outer
Loop (i): Runs 5 times to create 5 lines of
output.
2.
Inner
Loop (j): Runs 3 times (from 1 to 3) to print the
numbers "1 2 3" on each line.
The C Code
C
#include
<stdio.h>
int main() {
int i, j;
// Outer loop for the 5 rows
for (i = 1; i <= 5; i++) {
// Inner loop to print 1 2 3 in each row
for (j = 1; j <= 3; j++) {
printf("%d ", j);
}
// Move to the next line after printing 1 2 3
printf("\n");
}
return 0;
}
The Output
Plaintext
1 2 3
1 2 3
1 2 3
1 2 3
1 2 3
Key Takeaway
In your previous
examples, the inner loop often depended on the outer loop (like j <= k). Here, because the
inner loop condition j <= 3 is constant, every row
looks exactly the same.
Would you like to see
how to modify this so the numbers change per row (e.g., Row 1 is 1 1 1, Row 2 is 2 2 2)?
1. Write C programs to display the following patterns using nested loop construct.
(b)
1
2 1
1
2 1
1
2 1
1
2 1
1
2 1
Answer:
To
display this pattern, we need an outer loop to control the 5 rows and an inner loop that creates the sequence 1 2 1 in each row.
The Logic
Since the pattern
"1 2 1" is not a simple incrementing or decrementing line, we can
handle it in two ways:
1.
A single loop with a formula: Using an absolute value or a conditional to go up and back
down.
2.
Two small inner loops: One to count up to 2, and one to count back down to 1.
The C Code
Here is the most
straightforward way to write this using nested loops:
C
#include
<stdio.h>
int main() {
int i, j;
// Outer loop for 5 rows
for (i = 1; i <= 5; i++) {
// Inner loop 1: Count up from 1 to 2
for (j = 1; j <= 2; j++) {
printf("%d ", j);
}
// Inner loop 2: Count down starting from 1
for (j = 1; j >= 1; j--) {
printf("%d ", j);
}
printf("\n");
}
return 0;
}
The Output
Plaintext
1 2 1
1 2 1
1 2 1
1 2 1
1 2 1
Alternative (One Inner Loop)
If you want to be
clever, you can use a single loop from 1 to 3 and a small bit of math to flip
the 3 into a 1.
C
for (i = 1; i <= 5; i++) {
for (j = 1; j <= 3; j++) {
// If j is 3, print 1 instead
if (j == 3) printf("1 ");
else printf("%d ", j);
}
printf("\n");
}
Key Differences
·
The Two-Loop version is better if you ever want to expand
this to a larger palindrome (like 1
2 3 4 3 2 1).
·
The If-Statement version is slightly more concise for very
specific, short patterns.
Would you like to see
how to make this pattern increment with each
row (e.g., Row 1: 1 2 1, Row 2: 2
3 2)?
1. Write C programs to display the following patterns using nested loop construct.
(c)
4
3 2 1
4
3 2 1
4
3 2 1
4
3 2 1
4
3 2 1
Answer:
To create this
pattern, you need an outer loop to handle the 5 rows and an inner
loop that counts downward from 4 to 1.
The Logic
·
Outer
Loop (i): Runs 5 times (representing the rows).
·
Inner
Loop (j): Starts at 4 and continues as long as j \ge 1. In each step, j
is decremented (j--).
The C Code
C
#include
<stdio.h>
int main() {
int i, j;
// Outer loop for 5 rows
for (i = 1; i <= 5; i++) {
// Inner loop to count down from 4 to 1
for (j = 4; j >= 1; j--) {
printf("%d ", j);
}
// Move to the next line after each row
printf("\n");
}
return 0;
}
The Output
Plaintext
4 3 2 1
4 3 2 1
4 3 2 1
4 3 2 1
4 3 2 1
Key Takeaway
The direction of the
counting is controlled entirely by the inner loop's initialization and
update:
·
To count up: for (j =
1; j <= 4; j++)
·
To count down: for (j =
4; j >= 1; j--)
Would you like to see
how to make this count down starting from the row number (e.g.,
Row 5 starts at 5, Row 4 starts at 4)?
1. Write C programs to display the following patterns using nested loop construct.
(d)
2
2 3 4
2
3 4 5 6
Answer:
#include
<stdio.h>
int
main() {
int rows = 3;
for (int i = 1; i <= rows; i++) {
int num = 2;
// Print leading spaces for alignment
(optional, based on image alignment)
for (int space = 0; space < rows -
i; space++) {
printf(" ");
}
// Print numbers
for (int j = 1; j <= 2 * i - 1; j++)
{
printf("%d ", num++);
}
printf("\n");
}
return 0;
}
This code is a very clean way to generate the
triangle! By initializing int num =
2 inside the outer loop, you
ensure that every row starts fresh with the number 2.
How the Logic Breaks Down
1.
Row 1 (i=1):
o
Spaces: 3 - 1 = 2 spaces.
o
Numbers: Loop runs 2(1) - 1 = 1
time. Prints 2.
2.
Row 2 (i=2):
o
Spaces: 3 - 2 = 1 space.
o
Numbers: Loop runs 2(2) - 1 = 3
times. Prints 2 3 4.
3.
Row 3 (i=3):
o
Spaces: 3 - 3 = 0 spaces.
o
Numbers: Loop runs 2(3) - 1 = 5
times. Prints 2 3 4 5 6.
The Output
Your code will produce
this perfectly centered pyramid:
Plaintext
2
2 3 4
2 3 4 5 6
A Small Fix for the Header
In your snippet, you
have #include <stdio.h>. Ensure there is no line break between #include and <stdio.h>,
or the compiler will throw an error.
Why this structure is smart
By using num++ inside the j loop, you don't have
to worry about complex math like j
+ 1. The variable num simply keeps track of
the "next value to print" for that specific row.
One more variation for you:
What if you wanted the
numbers to continue counting instead of resetting to 2 every row?
You would simply move int num = 2; outside the loops:
C
int num = 2; // Moved outside
for (int i = 1; i <= rows; i++) {
// ... same space and j loops ...
}
New Output:
Plaintext
2
3 4 5
6 7 8 9 10
1. Write C
programs to display the following patterns using nested loop construct.
(e)
1
1 2 1
1 2 3 2 1
Answer:
This
is the Palindrome Pyramid, one of the most classic nested loop
challenges. It requires you to handle three distinct tasks in every row:
printing spaces, counting up, and then
counting down.
The Logic
To build a row like 1 2 3 2 1,
we break it into sections:
1. Spaces: Decreases as the row number increases (TotalRows - CurrentRow).
2. Ascending: A loop that counts from 1 up to the CurrentRow.
3. Descending: A loop that starts at CurrentRow - 1 and counts down to 1.
The C Code
C
#include <stdio.h>
int main() {
int rows = 3;
for (int i = 1; i <= rows; i++) {
// 1. Print leading spaces
for (int space = 1; space <= rows -
i; space++) {
printf(" ");
}
// 2. Print ascending numbers
for (int j = 1; j <= i; j++) {
printf("%d ", j);
}
// 3. Print descending numbers
// Starts at i-1 because the middle number is already printed
for (int j = i - 1; j >= 1; j--) {
printf("%d ", j);
}
printf("\n");
}
return 0;
}
The Output
Plaintext
1
1 2 1
1 2 3 2 1
Why this structure works
·
The
"Peak": The ascending loop
handles the peak of the pyramid (the highest number in the row).
·
The
Offset: The descending loop
starts at i - 1. If it started at i, you would get a
double peak (e.g., 1 2 3 3 2 1).
·
Alignment: Using two spaces in printf(" ") for the space loop matches the space used in printf("%d ", j) to keep the pyramid perfectly symmetrical.
Would you like to see
how to change this to use letters (A, ABA,
ABCBA) or should we try to make the pyramid larger?
1. Write C
programs to display the following patterns using nested loop construct.
(f)
*
* * *
* * * * *
* * * * * * *
* * * * *
* * *
*
Answer:
This is a Diamond (or Rhombus) Pattern built specifically with odd numbers of stars (1, 3, 5, 7, 5, 3, 1).
To create this, we
split the logic into two parts: the top half (where the
stars increase) and the bottom half (where
the stars decrease).
The Logic
·
Total
Rows: 7 (4 for the top, 3
for the bottom).
·
Star
Formula: For each row i, we
print (2i - 1) stars.
·
Space
Formula: To keep it centered,
we print (TotalRows - i) spaces.
The C Code
C
#include <stdio.h>
int main() {
int i, j, space;
int n = 4; // Number of rows for the top half
// 1. Top Half (including the middle line)
for (i = 1; i <= n; i++) {
// Spaces
for (space = 1; space <= n - i;
space++) printf(" ");
// Stars
for (j = 1; j <= (2 * i - 1); j++) printf("* ");
printf("\n");
}
// 2. Bottom Half
for (i = n - 1; i >= 1; i--) {
// Spaces
for (space = 1; space <= n - i;
space++) printf(" ");
// Stars
for (j = 1; j <= (2 * i - 1); j++) printf("* ");
printf("\n");
}
return 0;
}
The Output
Plaintext
*
* * *
* * * * *
* * * * * * *
* * * * *
* * *
*
### Key Techniques
* **The Inversion:**
Notice the second outer loop starts at `n - 1` and goes down to `1`. This
"flips" the math we used for the top half.
* **Symmetry:** Using
`2 * i - 1` ensures we only ever print an odd number of stars, which is
required to have a single "peak" star at the top and bottom.
Would you like to try
making this a **hollow diamond**, where only the outer border is made of stars?
1. Write C programs to display the following patterns using nested loop construct.
(g)
x x
x x x x
x x x x x x
x x x x x x x x
x x x x x x x x x x
Answer:
#include <stdio.h>
int main() {
int
i, j, rows = 5;
for
(i = 1; i <= rows; i++) {
for (j = 1; j <= i; j++) {
printf("x ");
}
for (j = 1; j <= 2 * (rows - i); j++) {
printf(" ");
}
for (j = 1; j <= i; j++) {
printf("x ");
}
printf("\n");
}
return 0;
}
This
code creates a Mirror Right-Angled Triangle (also
known as a "Butterfly" or "Canyon" pattern). It prints
characters on the far left and far right of the screen, with a shrinking gap of
spaces in the middle.
How the Logic Works
Each row is divided
into three distinct sections:
1.
Left Block (j <=
i): Prints 'x' characters
equal to the current row number.
2.
Middle Gap (j <=
2 * (rows - i)): Prints spaces. As i increases, the number
of spaces decreases, making the gap smaller.
3.
Right Block (j
<= i): Mirrors the left
block by printing 'x' characters again.
The Output
For
rows = 5, here is how it builds:
Plaintext
x x
x x x x
x x x x x x
x x x x x x x x
x x x x x x x x x x
Step-by-Step Breakdown
·
Row 1 ($i=1$): 1 'x', 8 spaces, 1 'x'.
·
Row 3 ($i=3$): 3 'x's, 4 spaces, 3 'x's.
·
Row 5 ($i=5$): 5 'x's, 0 spaces ($2 \times 0$), 5 'x's. (This forms a solid
line of 10 'x's).
Making it a full "Butterfly"
If
you want to complete the shape, you can copy the entire loop structure but
reverse the outer loop to count down from rows
- 1 to 1:
C
// Bottom half to
complete the butterfly
for (i = rows - 1; i >= 1; i--) {
for (j = 1; j <= i; j++) printf("x ");
for (j = 1; j <= 2 * (rows - i); j++) printf(" ");
for (j = 1; j <= i; j++) printf("x ");
printf("\n");
}
Would you like to see how to fill that middle gap with a different
character (like dots) to make it look like a bridge?
2.
Modify the solution of question no. 1 to accept the number of lines as the
input. The program should make the display pattern accordingly (Hint: write
separate programs).
(Question
No.1. Write C programs to display the following patterns using nested loop
construct.)
(a)
1 2 3
1 2 3
1 2 3
1 2 3
1 2 3
Answer:
#include <stdio.h>
int main() {
int
i, j, lines;
printf("Enter the number of lines: ");
scanf("%d", &lines);
for
(i = 1; i <= lines; i++) {
for (j = 1; j <= 3; j++) {
printf("%d ", j);
}
printf("\n");
}
return 0;
}
2.
Modify the solution of question no. 1 to accept the number of lines as the
input. The program should make the display pattern accordingly (Hint: write
separate programs).
(Question
No.1. Write C programs to display the following patterns using nested loop
construct.)
(b)
1 2 1
1 2 1
1 2 1
1 2 1
1 2 1
Answer:
#include <stdio.h>
int main() {
int i, j, lines;
printf("Enter the number of lines:
");
scanf("%d", &lines);
for (i = 1; i <= lines; i++) {
for (j = 1; j <= 2; j++) {
printf("%d ", j);
}
printf("\n");
}
return 0;
}
2.
Modify the solution of question no. 1 to accept the number of lines as the
input. The program should make the display pattern accordingly (Hint: write
separate programs).
(Question
No.1. Write C programs to display the following patterns using nested loop
construct.)
(c)
4
3 2 1
4
3 2 1
4
3 2 1
4
3 2 1
4
3 2 1
Answer:
#include <stdio.h>
int main() {
int
i, j, lines;
printf("Enter the number of lines: ");
scanf("%d", &lines);
for
(i = 1; i <= lines; i++) {
for (j = 4; j >= 1; j--) {
printf("%d ", j);
}
printf("\n");
}
return 0;
}
2.
Modify the solution of question no. 1 to accept the number of lines as the
input. The program should make the display pattern accordingly (Hint: write
separate programs).
(Question
No.1. Write C programs to display the following patterns using nested loop
construct.)
(d)
2
2 3 4
2 3 4 5 6
Answer:
#include <stdio.h>
int main() {
int i, j, lines;
printf("Enter the
number of lines: ");
scanf("%d",
&lines);
for (i = 0; i < lines;
i++) {
for (j = 2; j <= 4
+ i; j++) {
printf("%d
", j);
}
printf("\n");
}
return 0;
}
2.
Modify the solution of question no. 1 to accept the number of lines as the
input. The program should make the display pattern accordingly (Hint: write
separate programs).
(Question
No.1. Write C programs to display the following patterns using nested loop
construct.)
(e)
1
1 2 1
1 2 3 2 1
Answer:
#include <stdio.h>
int main() {
int
i, j, space, lines;
printf("Enter the number of lines: ");
scanf("%d", &lines);
for
(i = 1; i <= lines; i++) {
for (space = 1; space <= lines - i; space++) {
printf(" ");
}
for (j = 1; j <= i; j++) {
printf("%d ", j);
}
for (j = i - 1; j >= 1; j--) {
printf("%d ", j);
}
printf("\n");
}
return 0;
}
2.
Modify the solution of question no. 1 to accept the number of lines as the
input. The program should make the display pattern accordingly (Hint: write
separate programs).
(Question
No.1. Write C programs to display the following patterns using nested loop
construct.)
(f)
*
* * *
* * * * *
* * * * * * *
* * * * *
* * *
*
Answer:
#include <stdio.h>
int main() {
int i, j, space, lines;
printf("Enter the number of lines:
");
scanf("%d", &lines);
for (i = 1; i <= lines; i++) {
for (space = 1; space <= lines - i;
space++) {
printf(" ");
}
for (j = 1; j <= 2 * i - 1; j++) {
printf("*");
}
printf("\n");
}
return 0;
}
2.
Modify the solution of question no. 1 to accept the number of lines as the
input. The program should make the display pattern accordingly (Hint: write
separate programs).
(Question
No.1. Write C programs to display the following patterns using nested loop
construct.)
(g)
x x
x x x x
x x x x x x
x x x x x x x x
x x x x x x x x x x
Answer:
#include <stdio.h>
int main() {
int i, j, space, lines;
printf("Enter the number of lines:
");
scanf("%d", &lines);
for (i = lines; i >= 1; i--) {
for (space = 1; space <= lines - i;
space++) {
printf(" ");
}
for (j = 1; j <= i; j++) {
printf("X ");
}
printf("\n");
}
return 0;
}
3.
Extend the programs of Example 5.6 and Example 5.7 to make it dynamic by
accepting the number of lines as an input from the keyboard.
Example 5.6: A C
program to display a pattern.
#include <stdio.h>
int main()
{
int i, j, k, p;
for (k = 1; k <=5; k++)
{
for(i = 1; i<=(5-k); i++)
{
printf(" ");
}
for(j = 1; j <= (2*k - 1); j++)
{
printf("X");
}
printf("\n");
}
return 0;
}
Extend
the programs of Example 5.6 to make it dynamic by accepting the number of lines
as an input from the keyboard.
Answer:
To make Example 5.6
dynamic, we need to replace the fixed number 5 with a variable
(usually named n or rows). We will use the scanf() function to capture
this value from the user's keyboard.
The Dynamic Logic
1.
Input: We declare an integer variable n and ask the user to
provide a value.
2.
Space
Loop: Instead of 5 - k, the formula becomes n - k.
3.
Flexibility: The program will now work whether the user
enters 3, 10, or 50.
The Updated C Code
C
#include
<stdio.h>
int main() {
int i, j, k, n;
// 1. Accept input from the keyboard
printf("Enter the number of lines for the
pyramid: ");
scanf("%d", &n);
// 2. Outer loop runs 'n' times
for (k = 1; k <= n; k++) {
// 3. Print spaces based on the user's input
for (i = 1; i <= (n - k); i++) {
printf(" ");
}
// 4. Print 'X' based on the odd-number
formula
for (j = 1; j <= (2 * k - 1); j++) {
printf("X");
}
// Move to the next line
printf("\n");
}
return 0;
}
How the Dynamics Change the Output
If
you enter different values for n, the shape remains
a perfect pyramid but changes scale:
If n = 3:
Plaintext
X
XXX
XXXXX
If n = 6:
Plaintext
X
XXX
XXXXX
XXXXXXX
XXXXXXXXX
XXXXXXXXXXX
Key Programming Tip
When
using scanf(), always ensure you use the address-of operator (&)
before the variable name (e.g., &n). This tells the
computer exactly where in the memory to store the number the user types.
Example 5.7: A C
program to display a pattern
Answer:
#include <stdio.h>
int main()
{
int i, j, k;
for (k = 1; k <=5; k++)
{
for(i = 1; i<=(5-k); i++)
{
printf(" ");
}
for(j = 1; j <= (2*k - 1); j++)
{
printf("%d ", j);
}
printf("\n");
}
return 0;
}
Extend
the programs of Example 5.7 to make it dynamic by accepting the number of lines
as an input from the keyboard.
Answer:
To make Example 5.7
dynamic, we introduce a variable (typically n) to store the user's input. We then replace
the hard-coded limit of 5 with this variable in both the outer loop and
the space-calculating loop.
The Logic Adjustments
1.
Variable
Declaration: We add int n; to hold the number of
rows.
2.
Input
Function: We use scanf("%d", &n); to read the integer from the keyboard.
3.
Dynamic
Limits: * The outer loop now
runs until k <= n.
o The space loop prints (n - k) spaces.
The Updated C Code
C
#include
<stdio.h>
int main()
{
int i, j, k, n;
// Prompt user for input
printf("Enter the number of lines: ");
scanf("%d", &n);
// Outer loop for 'n' rows
for (k = 1; k <= n; k++)
{
// Inner loop for leading spaces
for (i = 1; i <= (n - k); i++)
{
printf(" ");
}
// Inner loop for numbers in each row
for (j = 1; j <= (2 * k - 1); j++)
{
printf("%d ", j);
}
// Move to the next line
printf("\n");
}
return 0;
}
Understanding the Change
When the program is
dynamic, the "center" of the pyramid shifts based on n.
·
If you enter 3, the first row has $3-1 = 2$ spaces.
·
If you enter 10, the first row has $10-1 = 9$ spaces.
A Quick Formatting Tip
Because you are
printing a space after the number (%d
), the pyramid will
naturally lean slightly to the right as it grows. To keep it perfectly balanced
for larger inputs, you can change the space loop to print two spaces: printf(" ");. This compensates for the two-character width (number + space)
of the output.
4. What is a nested loop? Why do
one use nested loops in our programs?
Answer:
A nested loop
is a loop inside another loop, where the inner loop runs completely for
each single iteration of the outer loop, used to process multi-dimensional data
(like grids/tables), generate patterns, or handle grouped items, making code efficient
for complex, layered tasks like iterating through rows and columns.
What is a Nested Loop?
·
It's a programming
structure where one loop (the inner loop) is placed within the body of another
loop (the outer loop).
·
For every single time
the outer loop executes, the inner loop runs from start to finish.
Why Use Nested Loops?
·
Multi-dimensional
Data: Ideal for
working with 2D arrays (like spreadsheets or matrices) where the outer loop
handles rows and the inner loop handles columns, visiting each element.
·
Complex
Patterns: Used to generate
visual patterns, such as triangles or grids of characters (e.g., *).
·
Combinations
& Groupings: Efficiently
create combinations of items or perform actions on groups within groups (e.g.,
finding all pairs in a list).
·
Structured
Repetition: Provides a
structured way to repeat operations across different levels, like processing
each day (outer) and then each period (inner) in a timetable.
·
Algorithmic
Tasks: Essential for
algorithms that require nested iterations, such as sorting algorithms or
searching through layered data structures.
Analogy: Think of a clock. The outer loop is the
hour hand (moving once an hour), and the inner loop is the minute hand
(completing 60 cycles for each hour the outer loop
advances).
5. Do we need to use same type of
loops as outer and inner loops? Justify your answer with some code segments.
Answer:
No, you don't need to
use the same type of loops (for, while, do-while) for your outer and inner
loops; any combination works, as the inner loop executes fully for each
iteration of the outer loop, making it useful for tasks like iterating over
rows and columns or processing data subsets, as shown in Python example and C# example where a for loop can contain a while loop. The choice depends on clarity and specific
logic, not mandatory matching.
Justification
·
Flexibility: Programming languages allow any loop
type within another because the inner loop's execution is treated as a single
block of code by the outer loop.
·
Suitability: You choose the loop type that best fits
the condition for that specific level of iteration
(e.g., for for known counts, while for conditional repetition).
·
Logic: The primary goal is clear logic; if
iterating through data structures (like lists of lists) or creating patterns,
different loops can express the process more naturally.
Code Examples (Python)
Example 1: for outer loop with while inner loop (Printing
patterns/matrix-like data)
python
# Outer loop iterates
through rows (0, 1, 2)
for
i in
range(3):
print(f"Outer loop iteration: {i}")
# Inner loop iterates for each row,
stopping when j reaches a certain condition
j = 0
while j < 2:
# Executes 2 times for each outer iteration
print(f" Inner loop: {j}")
j += 1
print("-" * 10)
Output: Prints 3 outer loops, each containing 2
inner loops.
Example 2: while outer loop with for inner loop (Processing data
conditionally)
python
# Outer loop continues
as long as condition is true
count
= 0
while
count < 2:
print(f"Outer while loop: {count}")
# Inner loop for a fixed number of items
(e.g., 3 colors)
for color
in ['Red',
'Green', 'Blue']:
print(f" Inner for loop: {color}")
count += 1
print("-" * 10)
Output: Demonstrates running a fixed set of
actions (for loop) multiple times (controlled
by while).
Example 3:
Common for (rows) and for (columns) (Grid/Matrix)
python
# Very common for
grid-like structures
for
row in
range(2):
for col
in range(3):
print(f"({row},{col})",
end=" ")
print() # Newline after each row
Output: (0,0) (0,1) (0,2) (1,0) (1,1) (1,2).
Answer No. 2:
The short answer is no. You do not need
to use the same type of loops for the outer and inner loops. This is known as nested loops, and you can mix and match for, while, and do-while loops (depending on your programming language) however
you see fit.
The choice of loop depends entirely on the logic of your problem, not on what the outer loop is
doing.
Why we mix loop types
We choose
a loop type based on how we need to iterate:
·
for
loops are best when you
know exactly how many times you need to run (e.g., iterating through a list or
a grid).
·
while loops are
best when you are waiting for a specific condition to change (e.g., waiting for
a user to type "exit" or a math calculation to reach a threshold).
Scenario 1: while
inside a for
Imagine you have a list of numbers (outer for loop), and for each number, you want to keep dividing it by 2
until it is less than 1 (inner while
loop).
Python
numbers = [10, 5, 20] for num in numbers: print(f"Processing number: {num}") # Inner loop is a 'while' because we don't know # how many divisions it will take beforehand. while num > 1: num = num / 2 print(f" Current value: {num}")Scenario 2: for
inside a while
Imagine a game that keeps running until the player quits (outer while loop). Inside the game, every turn, the player
"attacks" 3 enemies (inner for
loop).
Python
game_over = False while not game_over: print("--- New Turn ---") # Inner loop is a 'for' because the number # of enemies is fixed/known. for enemy in range(1, 4): print(f"Attacking enemy {enemy}!") # Logic to break the outer loop action = input("Type 'q' to quit or enter to continue: ") if action == 'q': game_over = TrueSummary Table
|
Outer Loop |
Inner Loop |
Is it allowed? |
Common Use Case |
|
|
|
Yes |
Standard grid/matrix processing. |
|
|
|
Yes |
Processing a list where each item needs conditional logic. |
|
|
|
Yes |
A main program loop that runs a fixed sequence of tasks. |
|
|
|
Yes |
Complex algorithms like searching a maze. |
Would you like me to help you write a specific nested loop for a
project or problem you're working on?
6. Can we put a third loop inside
the inner loop of a nested loop constract? Write a C program to justify your
answer.
Answer:
Yes, it is possible to
place a third (or more) loop inside the inner loop of a nested loop construct
in C programming. There is no language-specific restriction on the depth of
nesting [1].
The only practical
limitations are readability and maintainability of the code, and ensuring that
the logic handles the complexity correctly.
Here is a C program
that demonstrates a triply nested loop, printing combinations of numbers from 1
to 3 for each of the three loops:
#include
<stdio.h>
int
main() {
int i, j, k;
printf("Starting the triple nested
loop example:\n\n");
// Outer loop
for (i = 1; i <= 3; i++) {
// Inner loop
for (j = 1; j <= 3; j++) {
// Third, innermost loop
for (k = 1; k <= 3; k++) {
printf("i = %d, j = %d, k =
%d\n", i, j, k);
}
printf("\n"); // Add a
newline after the innermost loop finishes its iteration
}
printf("----------------------\n"); // Separator for the outer
loop iterations
}
printf("\nFinished the triple nested
loop example.\n");
return 0;
}
Justification and Output
When you compile and
run the above program, the output will look like this (abbreviated for
brevity):
Starting
the triple nested loop example:
i
= 1, j = 1, k = 1
i
= 1, j = 1, k = 2
i
= 1, j = 1, k = 3
i
= 1, j = 2, k = 1
i
= 1, j = 2, k = 2
i
= 1, j = 2, k = 3
i
= 1, j = 3, k = 1
i
= 1, j = 3, k = 2
i
= 1, j = 3, k = 3
----------------------
i
= 2, j = 1, k = 1
i
= 2, j = 1, k = 2
i
= 2, j = 1, k = 3
...
(continues for i=2 and i=3) ...
The output confirms that all 27
combinations (
3×3×33 cross 3 cross 3
3×3×3
) are executed, proving that the
third loop runs successfully inside the second (inner) loop [1].