iOS 阿拉伯数字转汉字数字（以及一些数字转一些特殊格式）

    int testNum = 3.7999;

    NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];

    formatter.numberStyle = kCFNumberFormatterRoundHalfDown;
    
    NSString *string = [formatter stringFromNumber:[NSNumber numberWithInt: testNum]];

typedef CF_ENUM(CFIndex, CFNumberFormatterRoundingMode) { 
  kCFNumberFormatterRoundCeiling = 0,  //四舍五入,直接输出4 
  kCFNumberFormatterRoundFloor = 1 ,    //保留小数输出3.8 
  kCFNumberFormatterRoundDown = 2,   //加上了人民币标志,原值输出￥3.8 
  kCFNumberFormatterRoundUp = 3,      //本身数值乘以100后用百分号表示,输出380% 
  kCFNumberFormatterRoundHalfEven = 4,//输出3.799999999E0 
  kCFNumberFormatterRoundHalfDown = 5,//原值的中文表示,输出三点七九九九。。。。
   kCFNumberFormatterRoundHalfUp = 6//原值中文表示,输出第四
};