In this C++ tutorial, you will learn how to find the value of e raised to power of given number minus 1 using expm1() function of cmath, with syntax and examples.

C++ expm1()

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

Syntax

The syntax of C++ expm1() is

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expm1(x)

where

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

Returns

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

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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.

Example

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

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

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

Output

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

Conclusion

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.