Difficulty using trignometric functions in iPhone app

in a开发者_C百科n iphone application i want to use the trignometic functions. but the answer is not coming correctly. this is my code:

#include"math.h"
double tri;
tri=sin(90);
printf("%lf",tri);

for this the answer is coming as 0.893977 how can i correct the code to get the answer as 1

double tri; 
tri=sin(90.0 * 3.1415926/180.0); 
printf("%lf",tri);

The arguments to standard trigonometric functions should be supplied in radians, not degrees.