iOS学习笔记: 每三个数字加一个逗号

//每三个数字加一个逗号 : 123,234,324

+ (NSString *)countNumAndChangeformat:(NSString *)num

{

    int count = 0;

    long long int a = num.longLongValue;

    while (a != 0) {

        count++;

        a /= 10;

    }

    NSMutableString *string = [NSMutableString stringWithString:num];

    NSMutableString *newstring = [NSMutableString string];

    while (count > 3) {

        count -= 3;

        NSRange rang = NSMakeRange(string.length - 3, 3);

        NSString *str = [string substringWithRange:rang];

        [newstring insertString:str atIndex:0];

        [newstring insertString:@"," atIndex:0];

        [string deleteCharactersInRange:rang];

    }

    [newstring insertString:string atIndex:0];

    return newstring;

}