Calculates the base 2 exponential of a number #include <math.h>
double exp2 ( double x );
float exp2f ( float x );
long double exp2l ( long double x );
The return value of the exp2( ) function is 2 raised to the power of the function's argument, or 2^{x}. If the result is beyond the range of the function's type, a range error occurs.  The base 2 exponential function exp2( ) is the inverse of the base 2 logarithm function, log2( ). 

Example
// The famous grainsofriceonachessboard problem.
// The sultan loses a chess game. The wager was one grain for square 1
// on the chessboard, then double the last number for each successive
// square. How much rice in all?
int squares = 64;
long double gramspergrain = 0.0025L; // A grain of rice weighs 25 mg.
long double sum = 0.0L;
for ( int i = 0; i < squares; i++ )
sum += gramspergrain * exp2l( (long double)i );
printf( "The sultan's wager costs him %.3Lf metric tons of rice.\n",
sum / 1000000.0L ); // A million grams per ton.
This code produces the following output:
The sultan's wager costs him 46116860184.274 metric tons of rice.
See Also
exp( ), expm1( ), log( ), log1p( ), log2( ), log10( )
