NSDecimalNumber

/**由于NSDecimalNumber能够存储很大的值（大到38位 x 10^+/-128）。这样进行一些大数值运算时也很方便，但是直接使用C的标量值会比通过NSDecimalNumber更快，所以需要慎重选择该方法。通常来说，这只在集合中使用。

     */

  

    //NSDecimalNumber常见用法

    //1.小数位处理及约数方式

    NSDecimalNumberHandler * roundUp = [NSDecimalNumberHandlerdecimalNumberHandlerWithRoundingMode:NSRoundBankersscale:2raiseOnExactness:NOraiseOnOverflow:NOraiseOnUnderflow:NOraiseOnDivideByZero:YES]; //保留两位小数（scale）

    /** RoundingMode：NSRoundPlain //貌似取整

        NSRoundDown, // Always down == truncate //只舍不入

        NSRoundUp, // Always up    // 只入不舍

        NSRoundBankers  // on a tie round so last digit is even  //貌似四舍五入

     **/

    NSDecimalNumber *subtotal = [NSDecimalNumberdecimalNumberWithString:@"90.7049"];

    NSDecimalNumber *discount = [NSDecimalNumberdecimalNumberWithString:@"0.22"];

    NSDecimalNumber *total = [subtotaldecimalNumberByAdding:discount withBehavior:roundUp];

    //按照roundUp规定好的进行相加：四舍五入、保留两位小数

    NSLog(@"Rounded total: %@", total);

    

    //2.次方计算

    NSDecimalNumber*price;

    price = [NSDecimalNumberdecimalNumberWithMantissa:1599exponent:-2  //10的－2次方

                    isNegative:NO];

    //等效于

    price = [NSDecimalNumberdecimalNumberWithString:@"15.99"];

   

    //3.加减乘除四则运算

    NSDecimalNumber*price1 = [NSDecimalNumberdecimalNumberWithString:@"15.99"];

    

    NSDecimalNumber*price2 = [NSDecimalNumberdecimalNumberWithString:@"29.99"];

    

    NSDecimalNumber*coupon = [NSDecimalNumberdecimalNumberWithString:@"5.00"];

    

    NSDecimalNumber*disCount = [NSDecimalNumberdecimalNumberWithString:@".90"];

    

    NSDecimalNumber*numProducts = [NSDecimalNumberdecimalNumberWithString:@"2.0"];

    

    NSDecimalNumber *subTotal = [price1decimalNumberByAdding:price2];//相加

    

    NSDecimalNumber *afterCoupon = [subtotaldecimalNumberBySubtracting:coupon];//相减

    

    NSDecimalNumber *afterDiscount = [afterCoupondecimalNumberByMultiplyingBy:disCount];//相乘

    //按照roundUp规定好的进行相乘：四舍五入、保留两位小数

    NSDecimalNumber*total2 = [subtotaldecimalNumberByMultiplyingBy:discountwithBehavior:roundUp];

    

    NSDecimalNumber *average = [afterDiscountdecimalNumberByDividingBy:numProducts];//相除

    

    NSDecimalNumber*averageSquared = [averagedecimalNumberByRaisingToPower:2];//平方

    

    

    //4.比较大小

    NSDecimalNumber*discount1 = [NSDecimalNumberdecimalNumberWithString:@".85"];

    

    NSDecimalNumber*discount2 = [NSDecimalNumberdecimalNumberWithString:@".9"];

    

    NSComparisonResult result = [discount1compare:discount2];

    

    if (result ==NSOrderedAscending) {

        

        NSLog(@"85%% < 90%%小于");

        

    } elseif (result == NSOrderedSame) {

        

        NSLog(@"85%% == 90%%等于");

        

    } elseif (result == NSOrderedDescending) {

        

        NSLog(@"85%% > 90%%大于");

        

    }