Entry vs Exit Controlled Loops

Entry controlled vs Exit controlled Loops

• An entry controlled loop is a loop in which the condition for executing the loop is checked at the beginning of the loop, before the code inside the loop is executed. for loop, while loop are entry controlled loop as they check the condition first before executing the code inside.

• An exit controlled loop is a loop in which the condition for executing the loop is checked at the end of the loop, after the code inside the loop has been executed. The do-while loop is an example of an exit controlled loop, because the condition for executing the loop is checked after the code inside the loop has been executed.

caution

Entry-controlled and Exit-controlled are not terms you will find officially in C documentation or books, These term are used to illustrate an idea and make an understanding of how the loop's control flow works

Examples of entry controlled loops

• A for loop that iterates 10 times:

#include <stdio.h>

int main()
{
    for (int i = 0; i < 10; i++)
    {
        printf("Iteration %d\n", i + 1);
    }
    return 0;
}

Output:

• A while loop that continues to execute while the value of a variable x is less than 5:

#include <stdio.h>

int main()
{
    int x = 0;
    while (x < 5)
    {
        printf("x is currently %d\n", x);
        x++;
    }

    return 0;
}

Output:

• A for loop that iterates over an array and prints out each element:

#include <stdio.h>

int main()
{
    int arr[] = {1, 2, 3, 4, 5};
    int n = sizeof(arr) / sizeof(arr[0]);
    for (int i = 0; i < n; i++)
    {
        printf("%d ", arr[i]);
    }

    return 0;
}

Output:

Examples of exit controlled loops

• A do-while loop that repeatedly asks the user to enter a number, and exits only when the user enters a negative number:

#include <stdio.h>

int main() {
    int num;

    do {
        printf("Enter a number: ");
        scanf("%d", &num);
        if (num >= 0) {
            printf("You entered %d\n", num);
        }
    } while (num >= 0);

    return 0;
}

• A do-while loop that keeps running until user enter 'y' or 'Y' for exit

#include <stdio.h>

int main() {

    char choice;
    do {
        // code to be executed
        printf("Do you want to exit? (y/n) ");
        scanf(" %c", &choice);
    } while (choice != 'y' && choice != 'Y');

    return 0;
}

• A do-while loop that continues to execute as long as a variable x is less than or equal to 3:

#include <stdio.h>

int main()
{
    int x = 0;
    do
    {
        printf("x is currently %d\n", x);
        x++;
    }
    while (x <= 3);

    return 0;
}

Output: