iOS 另外一个使用类的代码，四则运算，很简单，熟悉以下

//
//  main.m
//  0824-四则运算
//
//  Created by panba on 15-8-24.
//  Copyright (c) 2015年 panba. All rights reserved.
//

#import <Foundation/Foundation.h>
@interface calc:NSObject
-(void) setnum:(double) value;
-(void) clear;
-(double) calcnumreturn;
//算数方法
-(void) calcadd:(double) value;
-(void) calcsub:(double) value;
-(void) calcmul:(double) value;
-(void) calcdiv:(double) value;
@end

@implementation calc
{
    double calcnum;
}
-(void) setnum:(double)value
{
    calcnum = value;
}
-(void) calcadd:(double)value
{
    calcnum = calcnum + value;
}
-(void) calcsub:(double)value
{
    calcnum = calcnum - value;
}
-(void) calcdiv:(double)value
{
    calcnum = calcnum/value;
}
-(void) calcmul:(double)value
{
    calcnum = calcnum*value;
}

-(double) calcnumreturn
{
 return calcnum;
}

@end
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        double value1,value2;
        char oper;
        calc *calcnum = [[calc alloc] init];
        NSLog(@"input");
        scanf("%lf %c %lf",&value1,&oper,&value2);
        [calcnum setnum:value1];
        switch (oper) {
            case '+':
                [calcnum calcadd:value2];
                break;
            case '-':
                [calcnum calcsub:value2];
                break;
            case '/':
                [calcnum calcdiv:value2];
                break;
            case '*':
                [calcnum calcmul:value2];
                break;
            default:
                NSLog(@"error");
                break;
        }
        [calcnum calcnumreturn];
        NSLog(@"%lf",[calcnum calcnumreturn]);
    }
    return 0;
}