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For loop in C

The for loop is used when the number of iterations is known beforehand.

Flowchart:-

Syntax:

for(initialization; condition; incr/decr) {
    // Code to be executed
}
Example 1:
#include <stdio.h>

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

Output:

1
2
3
4
5
Example 2: Multiplication Table using for loop in C
#include <stdio.h>

int main() {
    int num;
    printf("Enter a number: ");
    scanf("%d", &num);

    for(int i = 1; i <= 10; i++) {
        printf("%d x %d = %d\n", num, i, num * i);
    }

    return 0;
}

Output:

Enter a number: 5

5 x 1 = 5
5 x 2 = 10
5 x 3 = 15
5 x 4 = 20
5 x 5 = 25
5 x 6 = 30
5 x 7 = 35
5 x 8 = 40
5 x 9 = 45
5 x 10 = 50

Difference

When we say, "we know beforehand," it means we already know how many times a loop should run before the loop starts execution. This is where a for loop is most useful.

When we don't know beforehand how many times the loop should run, we usually use a while or do-while loop. This happens when the loop depends on user input or a condition that isn't known before execution.

Example: Keep taking user input until user enters 0
#include <stdio.h>

int main() {
    int num;
    
    while(1) { 
        // Infinite loop, will break when user enters 0
        printf("Enter numbers (enter 0 to stop):\n");
        scanf("%d", &num);
        
        if (num == 0) {
            break; // Stop the loop if user enters 0
        }

        printf("You entered: %d\n", num);
    }

    printf("Loop stopped because you entered 0.\n");

    return 0;
}

Output:

Enter numbers (enter 0 to stop):
7
You entered: 7
Enter numbers (enter 0 to stop):
5
You entered: 5
Enter numbers (enter 0 to stop):
4
You entered: 4
Enter numbers (enter 0 to stop):
3
You entered: 3
Enter numbers (enter 0 to stop):
0
Loop stopped because you entered 0.

Explanation:

Here, we don't know beforehand how many times the user will enter numbers.
The loop continues until the user enters 0.
We use a while(1) infinite loop with a break statement to stop it when needed