C++ expm1()

C++ expm1() returns the value of e raised to power of given argument minus 1.


The syntax of C++ expm1() is



xA double, float, long double, or any integral type value.


The return value depends on the type of value passed for parameter x.

The return value of expm1(x) is

  • double if x is double or integral type.
  • float if x is float.
  • long double if x is long double.

The synopsis of expm1() function is

double expm1(double x);
float expm1(float x);
long double expm1(long double x);
double expm1(T x); // for integral type argument values

expm1() is a function of cmath library. Include cmath library in the program, if using expm1() function.


In this example, we read a value from user into variable x, and find the product of exponent raised to number x minus 1, using expm1() function.

C++ Program

#include <iostream>
using namespace std;

int main() {
    double x;
    cout << "Enter a number : ";
    cin >> x;
    double result = expm1(x);
    cout << "expm1(" << x << ") : " << result << endl;


Enter a number : 2
expm1(2) : 6.38906
Program ended with exit code: 0
Enter a number : 0
expm1(0) : 0
Program ended with exit code: 0
Enter a number : -5
expm1(-5) : -0.993262
Program ended with exit code: 0


In this C++ Tutorial, we learned the syntax of C++ expm1(), and how to use this function to find (e^x – 1), with the help of examples.