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# How to use log10( ) in C++

The log10() function is part of the cmath library in C++ – it allows you to take the logarithm of base 10 of any number.

Logarithm is a math function that finds out x by following the equation below.

$y = 10^{x}$

If y is given, we can find x by taking log10(y).

The following table defines the different outputs of the logarithm function.

Input y Output x
y > 1 positive value
y = 1 zero value
0 > y > 1 negative value
y = 0 $-\infty$
y < 0 not a number

The log10() function in cmath takes a number of any type in the argument and returns its base, 10 log. The returned value can be a float, double, long double or int.

Let’s see different examples of how the log10() function can be used.

#include <iostream>
#include <cmath>
using namespace std;

int main() {
// input output both of same type
double x0, y0 = 453.23;
x0 = log10(y0);
cout << "Log Base 10 of " << y0 << " is : " << x0 << endl;

//input output both of different type
double x1;
float y1 = 100.45;
x1 = log10(y1);
cout << "Log Base 10 of " << y1 << " is : " << x1 << endl;

// output as an integer
// notice that the output will discard any decimal places
int x2;
long double y2 = 4845645.85;
x2 = log10(y2);
cout << "Log Base 10 of " << y2 << " is : " << x2 << endl;

return 0;
}

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