C in a Nutshell

Name

exp

Synopsis

Calculates the natural exponential of a number

#include <math.h>
doubleexp( double x );
float expf( float x );
long double expl( long double x );

The return value of the exp() function is e raised to the power of the function’s argument, or e^x, where e is Euler’s number, 2.718281.... If the result is beyond the range of the function’s type, a range error occurs.

Tip

The natural exponential function exp() is the inverse of the natural logarithm function, log().

Example

/* Amount owed = principal * e**(interest_rate * time) */
int principal = 10000;      // Initial debt is ten thousand dollars.
int balance = 0;
double rate = 0.055;        // Interest rate is 5.5% annually.
double time = 1.5;          // Period is eighteen months.

balance = principal *exp( rate * time );
printf("Invest %d dollars at %.1f%% compound interest, and "
       "in %.1f years you'll have %d dollars.\n",
       principal, rate*100.0, time, balance );

This code produces the following output:

Invest 10000 dollars at 5.5% compound interest, and in 1.5 years
you'll have 10859 dollars.

See Also

The C99 exponential functions exp2() and expm1(); the exponential functions for complex numbers: cexp(), cexpf(), and cexpl(); the general exponential function, pow()