Tutorial

For loops in C are straightforward. They supply the ability to create a loop - a code block that runs multiple times. For loops require an iterator variable, usually notated as i.

For loops give the following functionality:

• Initialize the iterator variable using an initial value
• Check if the iterator has reached its final value
• Increases the iterator

For example, if we wish to iterate on a block for 10 times, we write:

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

This block will print the numbers 0 through 9 (10 numbers in total).

For loops can iterate on array values. For example, if we would want to sum all the values of an array, we would use the iterator i as the array index:

int array[10] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
int sum = 0;
int i;

for (i = 0; i < 10; i++) {
    sum += array[i];
}

/* sum now contains a[0] + a[1] + ... + a[9] */
printf("Sum of the array is %d\n", sum);

Exercise

Calculate the factorial (multiplication of all items array[0] to array[9], inclusive), of the variable array.

Tutorial Code

#include <stdio.h>

int main() {
  int array[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
  int factorial = 1;
  int i;

  /* calculate the factorial using a for loop  here*/

  printf("10! is %d.\n", factorial);
}

Expected Output

10! is 3628800.

Show Solution

#include <stdio.h>

int main() {
    int array[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
    int factorial = 1;

    int i;

    for(i=0;i<10;i++){
    factorial *= array[i];
    }

    printf("10! is %d.\n", factorial);
}