GFact | Putting a 0 before an integer constant

Predict the output of following program. C

#include <stdio.h>
int main() 
{
   int x = 012;
   printf("%d",  x);
   getchar();
   return 0;
}

The program prints 10. Putting a 0 before an integer constant makes it an octal number and putting 0x (or 0X) makes it a hexadecimal number. It is easy to put a 0 by accident, or as a habit. The mistake is very common with beginners.