? ? ? ? 在客戶端處理金額的時候，通常會涉及小數(shù)點后兩位有效數(shù)字，如果使用float和double的時候都會因為精度導(dǎo)致誤差的產(chǎn)生，不滿足金額對準確度的需求。蘋果為我們提供了NSDecimalNumber的API來處理貨幣計算的問題。
NSDecimalNumberHandler：
/**
數(shù)值格式設(shè)置
RoundingMode:? ? ? 舍入模式,有四種值：NSRoundUp(只入不舍), NSRoundDown(只舍不入), NSRoundPlain(四舍五入), NSRoundBankers(四舍六入, 中間值時, 取最近的,保持保留最后一位為偶數(shù))
scale: ? ? ? ? ? ? ? ? ? ? ? ?保留幾位小數(shù)
raiseOnExactness:? 發(fā)生精確錯誤時是否拋出異常，一般為NO
raiseOnOverflow:? ? 發(fā)生溢出錯誤時是否拋出異常，一般為NO
raiseOnUnderflow:? 發(fā)生不足錯誤時是否拋出異常，一般為NO
raiseOnDivideByZero: 除數(shù)是0時是否拋出異常，一般為YES
*/
NSDecimalNumberHandler *decimalNumberHandler = [NSDecimalNumberHandler decimalNumberHandlerWithRoundingMode:NSRoundPlain scale:2 raiseOnExactness:NO raiseOnOverflow:NO raiseOnUnderflow:NO raiseOnDivideByZero:YES];
NSDecimalNumber：NSDecimalNumber是NSNumber的子類，是蘋果針對浮點型計算時存在精度誤差的問題而提供的一個類。
/**
Mantissa:? 無符號長整型數(shù)值
exponent:? 指數(shù)（幾次方）
isNegative:是否是負數(shù)
result = Mantissa * 10^exponent
*/
NSDecimalNumber *dn1 = [NSDecimalNumber decimalNumberWithMantissa:36868 exponent:3 isNegative:NO];//36868000
NSDecimalNumber *dn2 = [NSDecimalNumber decimalNumberWithMantissa:36868 exponent:-3 isNegative:YES];//-36.868
NSLog(@"dn1 = %@,dn2 = %@",dn1,dn2);
//NSDecimalNumber 的使用。NSDecimalNumber是進行數(shù)值計算的對象，所有的加減乘除，冪運算等。
//123456789987654321.68 + 0.22 然后四舍五入
NSDecimalNumber *oneDecimalNumber = [[NSDecimalNumber alloc] initWithString:@"123456789987654321.68"];
NSDecimalNumber *twoDecimalNumber = [[NSDecimalNumber alloc] initWithString:@"0.22"];
//加
NSDecimalNumber *addRes = [oneDecimalNumber decimalNumberByAdding:twoDecimalNumber withBehavior:decimalNumberHandler];
//減
NSDecimalNumber *subtractRes = [oneDecimalNumber decimalNumberBySubtracting:twoDecimalNumber withBehavior:decimalNumberHandler];
//乘
NSDecimalNumber *multiplyingRes = [oneDecimalNumber decimalNumberByMultiplyingBy:twoDecimalNumber withBehavior:decimalNumberHandler];
//除
NSDecimalNumber *divideRes = [oneDecimalNumber decimalNumberByDividingBy:twoDecimalNumber withBehavior:decimalNumberHandler];
//n次方
NSDecimalNumber *powerResult = [twoDecimalNumber decimalNumberByRaisingToPower:2
withBehavior:decimalNumberHandler];
NSLog(@"%@\n %@\n %@\n %@\n %@\n",addRes,subtractRes,multiplyingRes,divideRes,powerResult);
//￥198.99 85折后
NSDecimalNumber *total = [NSDecimalNumber decimalNumberWithString:@"198.99"];
NSDecimalNumber *discount = [NSDecimalNumber decimalNumberWithString:@".85"];
NSDecimalNumber *pay = [total decimalNumberByMultiplyingBy:discount withBehavior:decimalNumberHandler];
NSLog(@"￥198.99 85折后應(yīng)付: ￥%@", pay);
//比較大小
NSDecimalNumber *num1 = [NSDecimalNumber decimalNumberWithString:@".3"];
NSDecimalNumber *num2 = [NSDecimalNumber decimalNumberWithString:@".9"];
NSComparisonResult result = [num1 compare:num2];
NSLog(@"num1 %@ num2", result > 0 ? @">":@"<");
