The function **double log10(double x);** returns the common logarithm of x. The common logarithm is the base-10 logarithm.

## Function prototype of log10

*double log10(double x);***x**: A floating point value whose logarithm to be calculated. It must be positive.

## Return value of log10

It returns the common logarithm of x. If x is negative, a domain error occurs.

## C program using log10 function

The following program shows the use of log10 function.

#include <stdio.h> #include <math.h> int main () { double x, result; /* Logarithm is only defined for positive numbers */ printf("Enter a positive number\n"); scanf("%lf", &x); result = log10(x); printf("Logarithm of %lf with base 10 is : %lf", x, result); return 0; }

Output

Enter a positive number 123 Logarithm of 123.000000 with base 10 is : 2.089905

Enter a positive number 100 Logarithm of 100.000000 with base 10 is : 2.000000