NSDecimalNumber是NSNumber的不可變子類。蘋果針對(duì)浮點(diǎn)型計(jì)算時(shí)存在精度計(jì)算誤差的問題而提供的一個(gè)計(jì)算類,它是基于10進(jìn)制的定點(diǎn)計(jì)算保證了精度不會(huì)缺失枢舶。同時(shí)也可以定制精度的取正類型：向上取正、向下去正、四舍五入等感耙。相對(duì)與浮點(diǎn)類型的計(jì)算荠医，NSDecimalNumber提供了更加精準(zhǔn)的計(jì)算吁脱。
一個(gè)定點(diǎn)數(shù)包含了：用一個(gè)尾數(shù)（Mantissa）、一個(gè)基數(shù)（Base）彬向、一個(gè)指數(shù)（Exponent）以及一個(gè)表示正負(fù)的符號(hào)(sign).
比如 15.99 用十進(jìn)制科學(xué)計(jì)數(shù)法可以表達(dá)為 +1599 × 10?2 兼贡，其中 1.2345 為尾數(shù)，10 為基數(shù)娃胆，2 為指數(shù)遍希。sign為 ‘+’。
代碼表示：
NSDecimalNumber*price;
price = [NSDecimalNumberdecimalNumberWithMantissa:1599
exponent:-2 ／／10的－2次方
isNegative:NO];
等效
price = [NSDecimalNumberdecimalNumberWithString:@"15.99"];
-
(NSDecimalNumber *)decimalNumberWithMantissa:(unsigned long long)mantissa exponent:(short)exponent isNegative:(BOOL)flag;
mantissa：長(zhǎng)整形里烦；exponent：指數(shù)凿蒜；flag：正負(fù)數(shù)。NSDecimalNumber *subtotalAmount = [NSDecimalNumber decimalNumberWithMantissa:1275 exponent:-2 isNegative:NO]; //12.75 subtotalAmount = [NSDecimalNumber decimalNumberWithMantissa:1275 exponent:2 isNegative:YES]; //-127500 -
(NSDecimalNumber *)decimalNumberWithDecimal:(NSDecimal)dcm;
將C語言NSDecimal類型轉(zhuǎn)成一個(gè)十進(jìn)制數(shù)胁黑。NSDecimalNumber *subtotalAmount = [NSDecimalNumber decimalNumberWithMantissa:1275 exponent:-2 isNegative:NO]; //12.75 NSDecimal decimalValue = [subtotalAmount decimalValue]; /** * 數(shù)據(jù)結(jié)構(gòu)： (NSDecimal) decimalValue = { _exponent = -2 _length = 1 _isNegative = 0 _isCompact = 1 _reserved = 0 _mantissa = ([0] = 1275, [1] = 0, [2] = 0, [3] = 0, [4] = 0, [5] = 0, [6] = 0, [7] = 0) } */ subtotalAmount = [NSDecimalNumber decimalNumberWithDecimal:decimalValue]; //12.75 -
(NSDecimalNumber *)decimalNumberWithString:(nullable NSString *)numberValue;
將字符串轉(zhuǎn)成一個(gè)十進(jìn)制數(shù)废封。NSDecimalNumber *discountAmount = [NSDecimalNumber decimalNumberWithString:@"-12.74"]; //-12.74 discountAmount = [NSDecimalNumber decimalNumberWithString:@"127.4"]; //127.4 -
(NSDecimalNumber *)decimalNumberWithString:(nullable NSString *)numberValue locale:(nullable id)locale;
這個(gè)有點(diǎn)復(fù)雜，locale代表一種格式丧蘸，就像date的格式化一樣漂洋。這里的locale可以傳遞兩種格式
NSDictionary類型：NSDictionary *locale = [NSDictionary dictionaryWithObject:@"," forKey:NSLocaleDecimalSeparator]; //以","當(dāng)做小數(shù)點(diǎn)格式 NSDecimalNumber *discountAmount = [NSDecimalNumber decimalNumberWithString:@"123,40" locale:locale]; //123.4 NSLocale *locale = [[NSLocale alloc] initWithLocaleIdentifier:@"fr_FR"]; //法國(guó)數(shù)據(jù)格式,法國(guó)的小數(shù)點(diǎn)是','逗號(hào) NSDecimalNumber *discountAmount = [NSDecimalNumber decimalNumberWithString:@"123,40" locale:locale]; //123.4+(NSDecimalNumber *)zero; //0 +(NSDecimalNumber *)one; //1 +(NSDecimalNumber *)minimumDecimalNumber; +(NSDecimalNumber *)maximumDecimalNumber; +(NSDecimalNumber *)notANumber; //非數(shù)字，常用于對(duì)比，比如： [[NSDecimalNumber notANumber] isEqualToNumber:myNumber];
加法運(yùn)算
-(NSDecimalNumber *)decimalNumberByAdding:(NSDecimalNumber *)decimalNumber;
-(NSDecimalNumber *)decimalNumberByAdding:(NSDecimalNumber *)decimalNumber withBehavior:(nullable id <NSDecimalNumberBehaviors>)behavior;
減法運(yùn)算
-(NSDecimalNumber *)decimalNumberBySubtracting:(NSDecimalNumber *)decimalNumber;
-(NSDecimalNumber *)decimalNumberBySubtracting:(NSDecimalNumber *)decimalNumber withBehavior:(nullable id <NSDecimalNumberBehaviors>)behavior;
乘法運(yùn)算
-(NSDecimalNumber *)decimalNumberByMultiplyingBy:(NSDecimalNumber *)decimalNumber withBehavior:(nullable id <NSDecimalNumberBehaviors>)behavior;
除法運(yùn)算
-(NSDecimalNumber *)decimalNumberByDividingBy:(NSDecimalNumber *)decimalNumber;
-(NSDecimalNumber *)decimalNumberByDividingBy:(NSDecimalNumber *)decimalNumber withBehavior:(nullable id <NSDecimalNumberBehaviors>)behavior;
a的n次方
-(NSDecimalNumber *)decimalNumberByRaisingToPower:(NSUInteger)power;
-(NSDecimalNumber *)decimalNumberByRaisingToPower:(NSUInteger)power withBehavior:(nullable id <NSDecimalNumberBehaviors>)behavior;
指數(shù)運(yùn)算
-(NSDecimalNumber *)decimalNumberByMultiplyingByPowerOf10:(short)power;
-(NSDecimalNumber *)decimalNumberByMultiplyingByPowerOf10:(short)power
withBehavior:(nullable id <NSDecimalNumberBehaviors>)behavior;
四舍五入運(yùn)算
-(NSDecimalNumber *)decimalNumberByRoundingAccordingToBehavior:(nullable id <NSDecimalNumberBehaviors>)behavior;
比較運(yùn)算
-(NSComparisonResult)compare:(NSNumber *)decimalNumber;
示例
NSDecimalNumber *discount1 = [NSDecimalNumber decimalNumberWithString:@"1.2"];
NSDecimalNumber *discount2 = [NSDecimalNumber decimalNumberWithString:@"1.3"];
NSComparisonResult result = [discount1 compare:discount2];
if (result == NSOrderedAscending) {
NSLog(@"1.2 < 1.3");
} else if (result == NSOrderedSame) {
NSLog(@"1.2 == 1.3");
} else if (result == NSOrderedDescending) {
NSLog(@"1.2 > 1.3");
}
加減乘除平方示例
NSDecimalNumber*price1 = [NSDecimalNumberdecimalNumberWithString:@"15.99"];
NSDecimalNumber*price2 = [NSDecimalNumberdecimalNumberWithString:@"29.99"];
NSDecimalNumber*coupon = [NSDecimalNumberdecimalNumberWithString:@"5.00"];
NSDecimalNumber*discount = [NSDecimalNumberdecimalNumberWithString:@".90"];
NSDecimalNumber*numProducts = [NSDecimalNumberdecimalNumberWithString:@"2.0"];
**加**
NSDecimalNumber *subtotal = [price1 decimalNumberByAdding:price2];
**減**
NSDecimalNumber *afterCoupon = [subtotal decimalNumberBySubtracting:coupon];
**除**
NSDecimalNumber *afterDiscount = [afterCoupon decimalNumberByMultiplyingBy:discount];
**平均**
NSDecimalNumber *average = [afterDiscount decimalNumberByDividingBy:numProducts];
平均價(jià)的平方
NSDecimalNumber*averageSquared = [average decimalNumberByRaisingToPower:2];
的NSLog（@“小計(jì)：％@”氮发，加后）;/ / 45.98
的NSLog（@“優(yōu)惠券后：％@”渴肉，減）;/ / 40.98
的NSLog（（@“折后：％@”），9/10）;/ / 36.882
的NSLog（@“每股平均價(jià)產(chǎn)品：％@”爽冕，平均）;/ / 18.441
的NSLog（@“平均價(jià)的平方：％@”仇祭，averageSquared）;/ / 340.070481
保留小數(shù)點(diǎn)后兩位
NSDecimalNumberHandler*roundUp = [NSDecimalNumberHandler
decimalNumberHandlerWithRoundingMode:NSRoundUp
scale:2
raiseOnExactness:NO
raiseOnOverflow:NO
raiseOnUnderflow:NO
raiseOnDivideByZero:YES];
//9折后 36.882 有余進(jìn)位結(jié)果 36.89
NSDecimalNumber*subtotal = [NSDecimalNumberdecimalNumberWithString:@"40.98"];
NSDecimalNumber*discount = [NSDecimalNumberdecimalNumberWithString:@".90"];
NSDecimalNumber*total = [subtotal decimalNumberByMultiplyingBy:discount
withBehavior:roundUp];
NSLog(@"Rounded total: %@", total);
