Stanford iphone development -CS193P Assignment 1 - "sin" operation

one of the required work is to implement the "sin" button on the calculator Add the following 4 operation buttons: • sin : calculates the sine of the top operand on the stack. here is my code ``` - (double)performOperation:(NSString *)operation { double result = 0; if ([operation isEqualToString:@"+"]) { result = [self popOperand] + [self popOperand]; }else if ([@"*" isEqualToString:operation]) { result = [self popOperand] * [self popOperand]; }else if ([operation isEqualToString:@"-"]) { double subtrahend = [self popOperand]; result = [self popOperand] - subtrahend; }else if ([operation isEqualToString:@"/"]) { double divisor = [self popOperand]; if(divisor) result = [self popOperand] / divisor; }else if([operation isEqualToString:@"sin"]){ double operd = [self popOperand]; NSLog(@"operd=%g",operd); if(operd) result = sin(operd); } [self pushOperand:result]; return result; } ``` I try to input sin(60) and the result=-0.304811 but actually I use calculator in windows and the result is 0.8860254 I don't know what's wrong with my code