What non-lethal code does antivirus usually run? (false positives)

I don’t know why, but I had no problems before that, and now all of a sudden this really old, terrible program for beginners, which I wrote a long time ago, starts Malwarebytes ... :(

This question is not a duplicate, since the program in question is in (ANSI) C and NOT Delphi ...

Here is a general virus scan (5/45)

Jotti Malware Scan (1/22)

Here is my crappy old source code: P

#include <stdio.h>
#include <string.h>
/* This script is by Joe DF*/
main()
{
    char input[999];
    int charcount = 100;
    gets(input);
    printf("%d\n", strlen(input));
    printf("%d", numlen(charcount));
}

numlen(int num)
{
    char temp[999];
    sprintf(temp, "%d", num);
    int count = strlen(temp);
    return count;
}

It may just be a mistake ... but why? It seems harmless to me! Even if it’s just a mistake, what usually causes a false positive? Is this just a file signature? Mark?