Why does a main function without a return statement return value 12?

I have written a program that prints a table. I have not included the return syntax in the main function, but still whenever I type echo $? it displays 12.

My source code :

#include <stdio.h>


int main(void)
{
    int ans,i,n;
    printf("enter the no. : ");
    scanf("%d",&n);

    for(i=1;i<=10;i++)
    {
        ans = n*i;
        printf("%d * %d = %d\n",n,i,ans);
    }
}

I have not written return 12, but still it returns 12 every time I execute the program.

Thanks.