# log() function in C++

In this tutorial, we will learn about **log function in C++**.

## log() function in C++

*log()* is the natural logarithmic function. It is the inverse of natural exponential function *(e).* When we use* log()* function, it returns the value with respect to base* e*. Another function similar to this is *log10()*. This gives us value with respect to base 10.

The syntax for the functions are :

log(x); log10(x);

We use the following header file with the functions :

#include <math.h>

The parameter *x* can be of *int, float, double* or *long double* type. We get return value as *float, double* or* long double* respectively. The return types of the parameters are as follows :

Parameter (x) | Return VALUE |
---|---|

x > 1 | Positive |

x = 1 | 0 |

0 > x > 1 | Negative |

x = 0 | -∞ (- infinity) |

x < 0 | NaN (Not a Number) |

Here is an example displaying the use of the* log()* and* log10()* functions in C++.

## A C++ program using log() and log10() functions :

#include<iostream> #include<math.h> using namespace std; int main() { double k, r, r10; cout << "Enter value of k : "; cin >> k; r = log(k); r10 = log10(k); cout << "log(k) = " << r << endl; cout << "log10(k) = " << r10 << endl; return 0; }

Output 1 :

Enter value of k : 6.2 log(k) = 1.82455 log10(k) = 0.792392

Output 2 :

Enter value of k : 0.54 log(k) = -0.616186 log10(k) = -0.267606

Hope this was helpful. Enjoy Coding!

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