Prototype: double log10(double anumber);
Header File: math.h (C) or cmath (C++)
Explanation: Log10 returns the logarithm for anumber, as long as it is not negative, or zero. To find the logarith of another base, use log base 10 of the number divided by log base 10 of the base to find the logarithm for.

//Example gives the log base ten of 100
#include <iostream>
#include <cmath>

using namespace std;

int main()
Other Functions