iOS开发之NSDecimalNumber货币计算

在iOS开发中，遇到和货币价格计算相关的，对计算精度要求比较高。使用float类型运算，经常出现误差。为了解决这种问题我们使用NSDecimalNumber。

一、基本算法

1、字符串初始化为NSDecimalNumber

NSDecimalNumber *number1 = [NSDecimalNumber decimalNumberWithString:@"123"];
NSDecimalNumber  *number2 = [NSDecimalNumber decimalNumberWithString:@"6.12"];

2、加法运算

NSDecimalNumber *num = [number2 decimalNumberByAdding:number1];

3、减法运算

NSDecimalNumber *num = [number1 decimalNumberBySubtracting:number2];

4、乘法运算

NSDecimalNumber *num = [number1 decimalNumberByMultiplyingBy:number2];

5、除法运算

NSDecimalNumber *num = [number1 decimalNumberByDividingBy:number2];

6、比较

if ([number1 compare:number2] == NSOrderedAscending) {
    
    NSLog(@"number1  <  number2");
}else if([number1 compare:number2] ==NSOrderedDescending){

    NSLog(@"number1  >  number2");
}else if ([number1 compare:number2] == NSOrderedSame){

    NSLog(@"number1  =  number2");
}

7、指数运算

NSDecimalNumber *num = [number1 decimalNumberByMultiplyingByPowerOf10:2];// number1乘10的2次方

// + (NSDecimalNumber *)decimalNumberWithMantissa:(unsigned long long)mantissa exponent:(short)exponent isNegative:(BOOL)flag;
// mantissa：长整形；exponent：指数；flag：正负数。
 NSDecimalNumber *subtotalAmount = [NSDecimalNumber decimalNumberWithMantissa:123 exponent:-2 isNegative:NO];// 1.23

8、次方运算

 NSDecimalNumber *num = [number1 decimalNumberByRaisingToPower:2];// number1的2次方 

二、保留小数位数及四舍五入

1、NSDecimalNumberHandler

NSDecimalNumberHandler *handler =[NSDecimalNumberHandler decimalNumberHandlerWithRoundingMode: NSRoundPlain
                                                                                                 scale:2
                                                                                      raiseOnExactness:NO
                                                                                       raiseOnOverflow:NO
                                                                                      raiseOnUnderflow:NO
                                                                                   raiseOnDivideByZero:YES];
[num decimalNumberByRoundingAccordingToBehavior:handler];

2、NSRoundingMode
NSRoundPlain, // Round up on a tie 四舍五入
NSRoundDown, // Always down == truncate 向下保留
NSRoundUp, // Always up 向上保留
NSRoundBankers // on a tie round so last digit is even (也是四舍五入,这是和NSRoundPlain不一样,如果精确的哪位是5,
它要看精确度的前一位是偶数还是奇数,如果是奇数,则入,偶数则舍,例如精确到小数点后两位, NSDecimalNumber 为1.225时,
NSRoundPlain结果为1.23,而NSRoundBankers则是1.22;NSDecimalNumber 为1.235时,均为1.24)
3、scale 保留小数个数
4、其它：溢出等是否报错