Solution of URI 1984 :: The Pronalância Puzzle

Before seeing the solution make sure that you tried enough. Don’t paste the whole code, just find out the logic. If you stuck in trouble, just inform me on comment.

/**Bismillahir Rahmanir Rahim.**/

#include <stdio.h>
#include <string.h>
int main()
{
    char num[25], temp;
    scanf("%s", num);
    int lnth = strlen(num);
    int i, j;
    for(i=0, j=lnth-1; i < lnth/2; i++, j--)
    {
        temp = num[i];
        num[i]=num[j];
        num[j]=temp;
    }
    printf("%s\n", num);
    return 0;
}