带有参数和返回值的对象方法

// 按要求设计计算器类

// 类的声明
#import <Foundation/Foundation.h>
@interface Calculator : NSObject 
// 没有属性不用写大括号{}
- (double) pi;
- (int) square:(int)num;    // 关于方法名的说明见下面
- (int) sumOfNum1:(int)num1 andNum2:(int)num2;    // 多个参数方法的写法注意见下面 
@end

// 类的实现
@implementation Calculator
- (double) pi {
        return 3.14159;
}
- (int) square:(int)num {
        return num * num;
}
- (int) sumOfNum1:(int)num1 andNum2:(int)num2 {
        return num1 + num2;
}
@end

// 类的调用
int main() {
        Calculator *cal = [Calculator new];

        double p = [cal pi];
        int sq  = [cal square:5];
        int sum = [cal sumOfNum1:5 andNum2:10];

        NSLog(@"The value of pi is %f", p);
        NSLog(@"Square of 5 is %d.", sq);
        NSLog(@"Sum of 5 and 10 is %d.", sum);

        return 0;
}