C Basics

C Program to Print Pattern Using While Loop: Step-by-Step Guide

In the previous section we discussed problems related to while loop. Now let us take a look at some more Problems.

1. Inverted Right Angle Triangle

Print the pattern below.

* * * * *

* * * *

* * *

* *

				
					#include <stdio.h>

int main() {
    int i = 5, j;

    while (i >= 1) {
        j = 1;
        while (j <= i) {
            printf("*");
            j++;
        }
        printf("\n");
        i--;
    }
    return 0;
}

// *****
// ****
// ***
// **
// *

Outer Loop (i)	Condition (i >= 1)	Inner Loop (j)	(j <= i)	Stars Printed
5	True	1, 2, 3, 4, 5	True (5 times)	*****
4	True	1, 2, 3, 4	True (4 times)	****
3	True	1, 2, 3	True (3 times)	***
2	True	1, 2	True (2 times)	**
1	True	1	True (1 times)	*
0	False	-	-	-

2. Repeated Number Pattern

333

4444

55555

				
					#include <stdio.h>

int main() {
    int i = 1, j;

    while (i <= 5) {
        j = 1;
        while (j <= i) {
            printf("%d", i);
            j++;
        }
        printf("\n");
        i++;
    }
    return 0;
}

// 1
// 22
// 333
// 4444
// 55555

Row (i)	Condition ( i <= 5)	Inner Loop (j)	Inner Condition (j <= i)	Result
1	True	1	1 <= 1 (True)	1
2	True	1, 2	1,2 <= 2 (True)	2, 2
3	True	1, 2, 3	1, 2, 3 <= 3 (True)	3, 3, 3
4	True	1, 2, 3, 4	1, 2, 3, 4 <= 4(True)	4, 4, 4, 4
5	True	1, 2, 3, 4, 5	1, 2, 3, 4, 5 <= 4(True)	5, 5, 5, 5, 5
6	False	-	-

3. Alphabet Pattern

ABC

ABCD

ABCDE

				
					#include <stdio.h>

int main() {
    int i = 1, j;

    while (i <= 5) {
        j = 1;
        while (j <= i) {
            printf("%c", 'A' + j - 1);
            j++;
        }
        printf("\n");
        i++;
    }
    return 0;
}

// A
// AB
// ABC
// ABCD
// ABCDE

Row (i)	Inner (j)	Calculation: 'A' + j - 1	Character Printed
1	1	'A' + 1 - 1 = 'A'	A
2	1, 2	'A'+0, 'A'+1	A, B
3	1, 2, 3	'A'+0, 'A'+1, 'A'+2	A, B, C
4	1, 2, 3, 4	'A'+0... 'A'+3	A, B, C, D
5	1, 2, 3, 4, 5	'A'+0... 'A'+4	A, B, C, D, E

4. Floyd’s Triangle

2 3

4 5 6

7 8 9 10

				
					#include <stdio.h>

int main() {
    int i = 1, j, num = 1;

    while (i <= 4) {
        j = 1;
        while (j <= i) {
            printf("%d ", num);
            num++;
            j++;
        }
        printf("\n");
        i++;
    }
    return 0;
}

// 1 
// 2 3 
// 4 5 6 
// 7 8 9 10

Row (i)	Condition ( i <= 4)	Inner Loop (j)	Value of num	Output
1	True	1	1 - > 2	1
2	True	1, 2	2 -> 3 -> 4	2 3
3	True	1, 2, 3	4 -> 5 -> 6 -> 7	4 5 6
4	True	1, 2, 3, 4	7 -> 8 -> 9 - > 10	7 8 9 10
5	False	-	-

5. Hollow Square

*****
* *
* *
* *
*****

				
					#include <stdio.h>

int main() {
    int i = 1, j;

    while (i <= 5) {
        j = 1;
        while (j <= 5) {
            if (i == 1 || i == 5 || j == 1 || j == 5)
                printf("*");
            else
                printf(" ");
            j++;
        }
        printf("\n");
        i++;
    }
    return 0;
}

// *****
// *   *
// *   *
// *   *
// *****

Row (i)	Row Type	Logic (Why?)	Visual Output
1	Top Boundary	i = 1 is True for all 5 stars	*****
2	Middle Section	Only j=1 and j=5 are True	* ___*
3	Middle Section	Only j=1 and j=5 are True	____
4	Middle Section	Only j=1 and j=5 are True	____
5	Bottom Boundary	i = 5 is True for all 5 stars	*****