CS0.101 - Computer Programming | C Pro Lecture 11

The lecture recording

Loops

A while loop simply checks the expression passed to it. It executes the code given repeatedly, checking the condition before every loop.

#include<stdio.h>

void main(void)
{
    int n;
    printf("Enter a number whose table you want printed: ");
    scanf("%d", &n);
    int i = 1;
    while(i <= 10) {
	printf("%d x %d = %d\n", i, n, i*n);
	i++;
    }
}

The above code executes till i becomes greater than 10.

while loops are straightforward, but sometimes for loops can be more convenient, or faster to write. They follow the syntax:

for ( initialization; check condition; updation ) {
    // some code here
    }

So if we were to write the same while loop as before using the for loop syntax, we would have:

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

There is also another kind of a loop known as a do while loop. It can be very handy in certain situations due to its readability. For example

int main()
{
    int digits = 0, n;
    printf("Enter a nonnegative integer: ");
    scanf("%d", &n);

    do {
	n /= 10;
	digits++;
    } while (n > 0);

    printf("The number has %d digits.\n", digits);

    return 0;
}

The do while loop also has the property that it is guaranteed to execute at least once. Since it is an exit controlled loop, it checks the condition after one execution of the loop, instead of before one execution.