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Basic
Switch Case
Goto
Operators
if Statement
Nested if
While Loop
For Loop
Patterns
Array
2D Array
String Function Example
Pointers
Recursion Function
Structure
Excersises
Others



C Program to Count Digits of a Number using Recursion


Write a C program to count digits of a number using recursion.

  • Take an integer input from the user and handle the special case when the number is 0.
  • Convert the number to positive if it's negative to simplify digit counting.
  • Use the recursion function countDigits() to count digits by dividing the number by 10 repeatedly.
  • Return the count by adding 1 at each recursion level until the base case (n == 0) is reached.
Example : pgm.c 
#include <stdio.h>

// Recursion function to count digits
int countDigits(int n) {
    if (n == 0)
        return 0;
    return 1 + countDigits(n / 10);
}

int main() {
    int num;

    printf("Enter an integer: ");
    scanf("%d", &num);

    if (num == 0) {
        printf("Number of digits: 1\n");
    } else {
        // Handle negative numbers
        if (num < 0)
            num = -num;

        printf("Number of digits: %d\n", countDigits(num));
    }

    return 0;
}

Output :

Enter an integer: 12345
Number of digits: 5