C Program to Count Number of Digits in an Integer

• Write a C program to count digits of a number.

Given an integer N, we have to count the number of digits of N and print it on screen.

For Example
Number of digits in 423536 is 6.

C program to count the number of digits in a number using loop

In this program, we first take a number as input from user using scanf function. Then inside while loop, we keep on removing right most digit(Least significant digit) of number and increment a counter(count variable) till number becomes zero. Finally, we print the value of count variable on screen.

/*
*  C program to count tne number of digits in an integer
*/
#include<stdio.h>
#include<conio.h>
 
int main() {
    int num, temp, count=0;
    printf("Enter an integer\n");
    scanf("%d", &num);
    temp = num;
     
    while(temp!=0) {
        temp = temp/10;
        ++count;
    }
    printf("Number of digits in %d : %d",num, count);
 
    getch();
    return 0;
}

Program Output

Enter an integer
12345
Number of digits in 12345 : 5

Enter an integer
-345
Number of digits in -345 : 3

C program to count the number of digits in a number using logarithm

We can use log10(logarithm of base 10) to count the number of digits of positive numbers (logarithm is not defined for negative numbers).
Digit count of N = log10(N) + 1

/*
*  C program to count the number of digits in an integer using logarithm
*/
#include<stdio.h>
#include<conio.h>
#include<math.h>
 
int main() {
    int num, temp;
    printf("Enter an integer\n");
    scanf("%d", &num);
    temp = num;
     
    /*If input number is negativ ethen make it positive */
    if(temp < 0)
       temp = temp*-1;
        
    if(temp) {
     /* If input number is non-zero */
        printf("Number of digits in %d : %d",num, (int)log10(temp)+1);
    } else {
        printf("Number of digits in %d : %d",num, 1);
    }
     
    getch();
    return 0;
}

Program Output

Enter an integer
6534
Number of digits in 6534 : 4

Enter an integer
-423
Number of digits in -423 : 3