通过NSNumberFormatter，设置NSNumber输出的格式

NSNumberFormatter *formatter = [[NSNumber Formatteralloc] init];

formatter.numberStyle =NSNumberFormatterDecimalStyle;

NSString *newAmount = [formatter stringFromNumber:[NSNumber numberWithint:123456789]];

（注意传入参数的数据长度，还可用double类型等）

NSNumberFormatter类有个属性numberStyle，是一个枚举型，设置不同的值可以输出不同的数字格式。该枚举包括：

enum{

NSNumberFormatterNoStyle = kCFNumberFormatterNoStyle,  

NSNumberFormatterDecimalStyle = kCFNumberFormatterDecimalStyle,

NSNumberFormatterCurrencyStyle = kCFNumberFormatterCurrencyStyle,

NSNumberFormatterPercentStyle = kCFNumberFormatterPercentStyle,

NSNumberFormatterScientificStyle = kCFNumberFormatterScientificStyle,

NSNumberFormatterSpellOutStyle = kCFNumberFormatterSpellOutStyle

};

各个枚举对应输出数字格式的效果如下：

123456789

123,456,789

￥123,456,789.00

-539,222,988%

1.23456789E8

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