log10() in C: Base-10 Logarithm

log10() returns the base-10 logarithm of a positive value. It answers questions such as “10 raised to what power gives this number?”

Syntax Top ↑

double log10(double x);

Powers of Ten Top ↑

#include <math.h>
#include <stdio.h>

int main(void) {
    printf("log10(1000) = %.1f\n", log10(1000.0));
    return 0;
}

Output

log10(1000) = 3.0

Number of Decimal Digits Top ↑

#include <math.h>
#include <stdio.h>

int main(void) {
    unsigned int value = 54321;
    int digits = (int)floor(log10((double)value)) + 1;

    printf("Digits: %d\n", digits);
    return 0;
}

This shortcut applies only to positive integers. Handle zero separately if adapting it for general input.

Subhendu Mohapatra

Author & Instructor at plus2net

I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.

About the author   Watch on YouTube

Connect: