NSDecimalNumber的加减乘除

    //number a
    NSDecimalNumber * a = [NSDecimalNumber decimalNumberWithString:@"2"];
    //number b
    NSDecimalNumber * b = [NSDecimalNumber decimalNumberWithString:@"2"];
    
    //加法
    NSDecimalNumber * add = [a decimalNumberByAdding:b];
    //减法
    NSDecimalNumber * subtract = [a decimalNumberBySubtracting:b];
    //乘法
    NSDecimalNumber * multiply = [a decimalNumberByMultiplyingBy:b];
    //除法
    NSDecimalNumber * divid = [a decimalNumberByDividingBy:b];

输出以上算法的结果： 屏幕快照 2020-04-16 16.06.44.png

NSDecimalNumberHandler：

/**
 初始化方法
 @param roundingMode 舍入方式
 @param scale 小数点后舍入值的位数
 @param exact 精度错误处理
 @param overflow 溢出错误处理
 @param underflow 下溢错误处理
 @param divideByZero 除以0的错误处理
 @return NSDecimalNumberHandler对象
 */
+ (instancetype)decimalNumberHandlerWithRoundingMode:(NSRoundingMode)roundingMode scale:(short)scale raiseOnExactness:(BOOL)exact raiseOnOverflow:(BOOL)overflow raiseOnUnderflow:(BOOL)underflow raiseOnDivideByZero:(BOOL)divideByZero;

NSRoundingMode 的类型

typedef NS_ENUM(NSUInteger, NSRoundingMode) {
    NSRoundPlain,   // Round up on a tie
    NSRoundDown,    // Always down == truncate
    NSRoundUp,      // Always up
    NSRoundBankers  // on a tie round so last digit is even
};

NSRoundPlain 是四舍五入
NSRoundDown 是向下取整
NSRoundUp 是向上取整
NSRoundBankers 是在四舍五入的基础上，加上末尾数为5时，变成偶数的规则

下面是我项目中的例子，具体的数值是：提现5.85元、费率为9%、单笔手续费一块钱

    //提现金额
    //手续费 = 提现金额*费率+单笔手续费
    //实际到账 = 提现金额 - 手续费
    //以下算法 货币类型 保证小数精度不丢失
    
    //要提现的金额 元
    NSDecimalNumber * amountValueNumber = [NSDecimalNumber decimalNumberWithString:money];
    NSString * singleFeeStr = [NSString stringWithFormat:@"%@",accountInfo.singleFee];
    NSDecimalNumber * singFeeValueNumber = [NSDecimalNumber decimalNumberWithString:singleFeeStr];
    //费率转换：除以100
    NSDecimalNumber * singFeeHundredNumber = [NSDecimalNumber decimalNumberWithString:[NSString stringWithFormat:@"%d", 100]];
    NSDecimalNumber * singleFeeNumber = [singFeeValueNumber decimalNumberByDividingBy:singFeeHundredNumber];
    
     //费率 eg:3% 以下费率相关都用3距离
    NSString * rateStr = [NSString stringWithFormat:@"%@%%",accountInfo.rate];
    //费率：3
    NSDecimalNumber * rateValueNumber = [NSDecimalNumber decimalNumberWithString:rateStr];
    //费率转换：除以100
    NSDecimalNumber *oneHundredValueNumber = [NSDecimalNumber decimalNumberWithString:[NSString stringWithFormat:@"%d", 100]];
    //费率转小数：0.03
    NSDecimalNumber *rate = [rateValueNumber decimalNumberByDividingBy:oneHundredValueNumber];
    //根据费率产生的手续费(四舍五入之前数值)
    NSDecimalNumber *fee = [amountValueNumber decimalNumberByMultiplyingBy:rate];
    //四舍五入之后的手续费
    NSDecimalNumberHandler *roundingBehavior = [NSDecimalNumberHandler decimalNumberHandlerWithRoundingMode:NSRoundPlain scale:2 raiseOnExactness:NO raiseOnOverflow:NO raiseOnUnderflow:NO raiseOnDivideByZero:NO];
    NSString *feeStr =[[fee decimalNumberByRoundingAccordingToBehavior:roundingBehavior] stringValue];
    //需求上手续费需要四舍五入
    NSDecimalNumber * feeDecimal = [NSDecimalNumber decimalNumberWithString:feeStr];
    
    //总手续费 费率手续费+单笔
    NSDecimalNumber * totalFeeNumber = [feeDecimal decimalNumberByAdding:singleFeeNumber];
    NSDecimalNumber * actualDecimal = [amountValueNumber decimalNumberBySubtracting:totalFeeNumber];
    NSLog(@"\n四舍五入之前的手续费%@\n提现金额%@\n提现费率%@\n手续费%@\n单笔加%@\n实际到账%@",fee,amountValueNumber,rateStr,feeDecimal,singleFeeNumber,actualDecimal);

输出的具体数值：

屏幕快照 2020-04-16 16.49.24.png