C Program to Count Number of Digits in an Integer

This program takes an integer from the user and calculates the number of digits. For example: If the user enters 2319, the output of the program will be 4.

Program to Count the Number of Digits

#include <stdio.h>
int main() {
  long long n;
  int count = 0;
  printf("Enter an integer: ");
  scanf("%lld", &n);
 
  // iterate at least once, then until n becomes 0
  // remove last digit from n in each iteration
  // increase count by 1 in each iteration
  do {
    n /= 10;
    ++count;
  } while (n != 0);

  printf("Number of digits: %d", count);
}

Output

Enter an integer: 3452
Number of digits: 4

The integer entered by the user is stored in variable n. Then the do...while loop is iterated until the test expression n! = 0 is evaluated to 0 (false).

• After the first iteration, the value of n will be 345 and the count is incremented to 1.
• After the second iteration, the value of n will be 34 and the count is incremented to 2.
• After the third iteration, the value of n will be 3 and the count is incremented to 3.
• After the fourth iteration, the value of n will be 0 and the count is incremented to 4.
• Then the test expression of the loop is evaluated to false and the loop terminates.

Note: We have used a do...while loop to ensure that we get the correct digit count when the user enters 0.