IOS 关于四舍五入的神器NSDecimalNumber

如何只舍不入。比如 float price = 0.126，怎么样才能得到0.12？

当然，通过字符串截取的办法肯定也能达到相同的效果。但是就是这么一个简单的问题要通过一些判断和截取才能获得结果，总感觉有点笨拙。

下面先给出该问题的解决办法：

-(NSString *)notRounding:(float)price afterPoint:(int)position{

    NSDecimalNumberHandler* roundingBehavior = [NSDecimalNumberHandler decimalNumberHandlerWithRoundingMode:NSRoundDown scale:position raiseOnExactness:NO raiseOnOverflow:NO raiseOnUnderflow:NO raiseOnDivideByZero:NO];

    NSDecimalNumber *ouncesDecimal;

    NSDecimalNumber *roundedOunces;

    

    ouncesDecimal = [[NSDecimalNumber alloc] initWithFloat:price];

    roundedOunces = [ouncesDecimal decimalNumberByRoundingAccordingToBehavior:roundingBehavior];

    [ouncesDecimal release];

    return [NSString stringWithFormat:@"%@",roundedOunces];

}

介绍一下参数：

price:需要处理的数字，

position：保留小数点第几位，

然后调用

    float s =0.126;

    NSString *sv = [self notRounding:s afterPoint:2];

    NSLog(@"sv = %@",sv);

输出结果为：sv = 0.12

接下来介绍NSDecimalNumberHandler初始化时的关键参数：decimalNumberHandlerWithRoundingMode：NSRoundDown，

NSRoundDown代表的就是 只舍不入。

scale的参数position代表保留小数点后几位。

如果只入不舍怎么办，比如，float 0.162 想要得到0.17该怎么做？，在开发文档上有这样一个表，是按照保留小数点后一位处理的。相信大家一看就明白了：

方法二:

1、round(12345.6789) 结果为：12346

2、round(12345.6789*100)/100 结果为：12345.68

第二个是我要的结果，但是我不明白这么个简单的四舍五入要搞的这么复杂，应该有更好的吧，我记得在其他语言里用：round(12345.6789，2) 就可以实现四舍五入到两位小数。

方法三:

NSTimeInterval Interval = 305.721125;

NSInteger timeInt = [[NSString stringWithFormat:@"%.0f", Interval] integerValue];

 

Interval:305.721125

timeInt:306

1	NSLog(@"%@", [NSString stringWithFormat:@"%.0f", 1.0003]);

2	NSLog(@"%@", [NSString stringWithFormat:@"%.0f", 1.9003]);

3	NSLog(@"%@", [NSString stringWithFormat:@"%.0f", 1.5003]);

4	NSLog(@"%@", [NSString stringWithFormat:@"%.0f", 1.4003]);

1

1

1

1

1

2

1

2

1

1

方法四:

　　

1. /

    //Test "/"
    cout << "Test \"/\"!" << endl;
    cout << "7   / 2   = " << 7/2 << endl;      //3
    cout << "7   / 2.0 = " << 7/2.0 << endl;    //3.5
    cout << "7.0 / 2   = " << 7.0/2 << endl;    //3.5
    cout << "7.0 / 2.0 = " << 7.0/2.0 << endl; //3.5
    cout << "7   / 3   = " << 7/3 << endl;      //2
    cout << endl;

2. %
    //Test "%"
    cout << "Test \"%\"!" << endl;
    cout << "9   % 3   = " << 9%3 << endl;      //0
    cout << "9   % 4   = " << 9%4 << endl;      //1
    //cout << "9.0 % 3   = " << 9.0%3 << endl;
    //cout << "9   % 3.0 = " << 9%3.0 << endl;
    cout << endl;

3. 四舍五入
    //Test round()
    cout << "Test \"四舍五入\"!" << endl;
    double dRoundA = 1.4;
    double dRoundB = 1.6;
    double dRoundLowA = -1.4;
    double dRoundLowB = -1.6;
    double dRoundLowC = 0.0;
    cout << dRoundA << " = " << RoundEx(dRoundA) << endl;         //1
    cout << dRoundB << " = " << RoundEx(dRoundB) << endl;         //2
    cout << dRoundLowA << " = " << RoundEx(dRoundLowA) << endl;   //-1
    cout << dRoundLowB << " = " << RoundEx(dRoundLowB) << endl;   //-2
    cout << dRoundLowC << " = " << RoundEx(dRoundLowC) << endl;   //0
    cout << endl;

double RoundEx(const double& dInput)
{
    double dIn = dInput;
    if (dInput >= 0.0)    //???
    {
        return int(dIn + 0.5);
    } 
    else
    {
        return int(dIn - 0.5);
    }
}

4. ceil() 向上取整
    //Test ceil() 向上取整
    cout << "Test ceil() 向上取整!" << endl; 
    cout << "ceil 1.2 = " << ceil(1.2) << endl;      //2
    cout << "ceil 1.8 = " << ceil(1.8) << endl;      //2
    cout << "ceil -1.2 = " << ceil(-1.2) << endl;    //-1
    cout << "ceil -1.8 = " << ceil(-1.8) << endl;    //-1
    cout << "ceil 0.0 = " << ceil(0.0) << endl;      //0
    cout << endl;

5. floor() 向下取整
    //Test floor() 向下取整
    cout << "Test floor() 向下取整!" << endl;
    cout << "floor 1.2 = " << floor(1.2) << endl;    //1
    cout << "floor 1.8 = " << floor(1.8) << endl;    //1
    cout << "floor -1.2 = " << floor(-1.2) << endl; //-2
    cout << "floor -1.8 = " << floor(-1.8) << endl; //-2
    cout << "floor 0.0 = " << floor(0.0) << endl;    //0
    cout << endl;