Here is another problem from K&R , I have been sittin with it for 4 hours

This program tried to concatenate two strings. It aint doin it


Code:
#include "stdio.h"

int  str_cat(char *, char *);

int main()
{
        char *str1 = "saguna";
        char *str2 = "karan";
         str_cat(str1,str2);
        return 0;
} //main closes

int   str_cat(char *st1, char *st2)
{
        for(; *st1 != '\0'; st1++)
        {
                if(*st1 == '\0')
                {
                        printf("check ");          //not goin in if statement, it goes till s
                        for(;*st2 != '\0';st2++)
                        {
                         *st2 == *st1;
                        }
                        printf("The value of *st2=\n\n\n\n\n%c",*st2);
                         //return *st2;
                }
                else
                {
                        printf("\nsomethings wronng\n");
                }
        }
} //str_cat closes
Kindly help. I have tried my best