# C program to count digits of a number using logarithms

• Write a program in C to count digits of a number without using loops or conditional operator.
• How to find number of digits in an integer using common logarithms.

To count the digits of a number, we can use common logarithms(base 10). Here is the formulae to find number of digits of a positive integer.

Digit count of N = (int)(log10(N) + 1)


As logarithm is only defined for positive numbers, we have to first convert negative numbers to positive numbers by multiplying then by -1.

For Example:

Digit count of 1234 = (int)(log(1234) + 1) = (int)(3.091 + 1) = 4


### C program to count digits of a number using common logarithms /*
C Program to count number of digits in an integer in
one line
*/
#include<stdio.h>
#include<math.h>

int main() {
int num, digitCount;

printf("Enter a positive integer\n");
scanf("%d", &num);

if(num < 0) num = num *-1;
if(num){
/* number of digit = log10(n) + 1 */
digitCount = (int)log10((double)num) + 1;
} else {
digitCount = 1;
}
printf("Digit Count = %d", digitCount);
return 0;
}

Output

Enter an integer
2345
Digit Count = 4

Enter an integer
-234
Digit Count = 3

Enter an integer
0
Digit Count = 1