通过NSNumberFormatter，设置NSNumber输出的格式
NSNumberFormatter *formatter = [[NSNumberFormatteralloc]init];
formatter.numberStyle =NSNumberFormatterDecimalStyle;
NSString *newAmount = [formatterstringFromNumber:[NSNumbernumberWithint: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
一亿二千三百四十五万六千七百八十九