iOS01 计算器

        #import "ViewController.h"  

        @interface ViewController ()
        {
            UILabel *_display;
            NSString *_operator1;
            NSString *_operator;
            NSString *_operator2;
        }
        @end  

        @implementation ViewController  

        - (void)viewDidLoad
        {
            [super viewDidLoad];
            // Do any additional setup after loading the view, typically from a nib.
            //创建UI界面
            _display = [[UILabel alloc] initWithFrame:CGRectMake(10, 50, self.view.frame.size.width-20, 100)];
            _display.backgroundColor = [UIColor grayColor];
            _display.alpha = 0.8;
            _display.textAlignment = NSTextAlignmentRight;
            _display.numberOfLines = 2;
            _display.text = @"";
            _operator = @"";
            _operator1 = @"";
            _operator2 = @"";
            [self.view addSubview:_display ];
            NSArray *titleArray1 = @[@"MC",@"M+",@"M-",@"MR",@"清除"];
            NSArray *titleArray2 = @[@[@"7",@"8",@"9",@"+"],@[@"4",@"5",@"6",@"-"],@[@"1",@"2",@"3",@"*"],@[@"0",@".",@"=",@"/"]];
            CGFloat size1 = (self.view.frame.size.width-60)/5;
            CGFloat size2 = (self.view.frame.size.width-50)/4;
            for (int i=0; i<5; i++)
            {
                CGRect frame = CGRectMake(10+i*(size1+10), 180, size1, 50);
                [self createButtonByFrame:frame withTitle:titleArray1[i]];
            }
            for (int i=0; i<4; i++)
            {
                for (int j=0; j<4; j++)
                {
                    [self createButtonByFrame:CGRectMake(10+j*(size2+10), 240+i*60, size2, 50) withTitle:titleArray2[i][j]];
                }
            }
        }  

        - (void)createButtonByFrame:(CGRect)frame withTitle:(NSString *)title
        {
            UIButton *btn = [UIButton buttonWithType:UIButtonTypeSystem];
            btn.frame = frame;
            btn.backgroundColor = [UIColor grayColor];
            btn.alpha = 0.8;
            btn.layer.cornerRadius = 10;
            [btn setTitle:title forState:UIControlStateNormal];
            btn.titleLabel.font = [UIFont systemFontOfSize:25];
            [btn setTitleColor:[UIColor blueColor] forState:UIControlStateNormal];
            [btn addTarget:self action:@selector(btnClicked:) forControlEvents:UIControlEventTouchUpInside];  

            [self.view addSubview:btn];
        }  

        - (void)btnClicked:(UIButton *)btn
        {
            NSString *title = btn.currentTitle;
            if ([title hasPrefix:@"M"])
            {  

            }
            if ([title isEqualToString:@"清除"])
            {
                _display.text = @"";
                _operator = @"";
                _operator1 = @"";
                _operator2 = @"";
                return;
            }
            if ([self isOperator:title])
            {
                if (_operator.length)//判断操作运算符是否已经存在
                {
                    float result = 0.0;
                    float value1 = [_operator1 floatValue];
                    float value2 = [_operator2 floatValue];
                    unichar ch = [_operator characterAtIndex:0];
                    switch (ch)
                    {
                        case ‘+‘:
                            result = value1+value2;
                            break;
                        case ‘-‘:
                            result = value1-value2;
                            break;
                        case ‘*‘:
                            result = value1*value2;
                            break;
                        case ‘/‘:
                            result = value1/value2;
                            break;
                        default:
                            break;
                    }
                    _operator1 = [NSString stringWithFormat:@"%g",result];
                    _display.text = [NSString stringWithFormat:@"%@\n%@",_operator1,title];
                    _operator2 = @"";
                    if ([btn.currentTitle isEqualToString:@"="])
                    {
                        _operator = @"";
                    }
                    else
                    {
                        _operator = title;
                    }
                }
                else
                {
                    _operator = title;
                    _display.text = [NSString stringWithFormat:@"%@\n%@",_operator1,_operator];
                }
            }
            else//是操作数
            {
                if (_operator.length)//判断是哪个操作数
                {
                    if ([_operator2 containsString:@"."] && [title isEqualToString:@"."])
                    {  

                    }
                    else
                    {
                        _operator2 = [_operator2 stringByAppendingString:title];
                        _display.text = [NSString stringWithFormat:@"%@\n%@%@",_operator1,_operator,_operator2];
                    }
                }
                else
                {
                    if ([_operator1 containsString:@"."] && [title isEqualToString:@"."])
                    {  

                    }
                    else
                    {
                        _operator1 = [_operator1 stringByAppendingString:title];
                        _display.text = _operator1;
                    }
                }
            }
        }  

        //判断标题是否为运算符+ - * / =
        - (BOOL)isOperator:(NSString *)title
        {
            if ([[NSCharacterSet characterSetWithCharactersInString:@"+-*/="] characterIsMember:[title characterAtIndex:0]])
            {
                return YES;
            }  

            return NO;
        }
        - (void)didReceiveMemoryWarning {
            [super didReceiveMemoryWarning];
            // Dispose of any resources that can be recreated.
        }
        @end