通過NSNumberFormatter，設置NSNumber輸出的格式
NSNumberFormatter *formatter = [[NSNumberFormatteralloc]init];
formatter.numberStyle =NSNumberFormatterDecimalStyle;
NSString *newAmount = [formatterstringFromNumber:[NSNumbernumberWithint:123456789]];
（注意傳入參數的數據長度，還可用double類型等）
NSNumberFormatter類有個屬性numberStyle，是一個枚舉型，設置不同的值可以輸出不同的數字格式。該枚舉包括：
enum{
NSNumberFormatterNoStyle = kCFNumberFormatterNoStyle,
NSNumberFormatterDecimalStyle = kCFNumberFormatterDecimalStyle,
NSNumberFormatterCurrencyStyle = kCFNumberFormatterCurrencyStyle,
NSNumberFormatterPercentStyle = kCFNumberFormatterPercentStyle,
NSNumberFormatterScientificStyle = kCFNumberFormatterScientificStyle,
NSNumberFormatterSpellOutStyle = kCFNumberFormatterSpellOutStyle
};
各個枚舉對應輸出數字格式的效果如下：
123456789
123,456,789
￥123,456,789.00
-539,222,988%
1.23456789E8
一億二千三百四十五萬六千七百八十九