I had this problem on an exam yesterday. I couldn't resolve it so you can imagine the result...

Make a recursive function: int invertint( int num) that will receive an integer and return it but inverted, example: 321 would return as 123

I wrote this:

int invertint( int num ) {
  int rest = num % 10;
  int div = num / 10;
  if( div == 0 ) {
     return( rest );
  }
  return( rest * 10 + invert( div ) )
}

Worked for 2 digits numbers but not for 3 digits or more. Since 321 would return 1 * 10 + 23 in the last stage.

Thanks a lot!

PS: Is there a way to understand these kind of recursion problems in a faster manner or it's up to imagination of one self?