iOS 数字每隔3位添加一个逗号的

+(NSString *)countNumAndChangeformat:(NSString *)num
{
    int count = ;
    long long int a = num.longLongValue;
    while (a != )
    {
        count++;
        a /= ;
    }
    NSMutableString *string = [NSMutableString stringWithString:num];
    NSMutableString *newstring = [NSMutableString string];
    while (count > ) {
        count -= ;
        NSRange rang = NSMakeRange(string.length - , );
        NSString *str = [string substringWithRange:rang];
        [newstring insertString:str atIndex:];
        [newstring insertString:@"," atIndex:];
        [string deleteCharactersInRange:rang];
    }
    [newstring insertString:string atIndex:];
    return newstring;
}

例：123456789

结果：123，456，789