#include <stdio.h>
    #include <stdlib.h> //for malloc
    #include <string.h>

    int *my_strcat(const char* const str1, const char *const str2)
    {
    	int s1, s2, s3, i=0;
    	char *a;
    	s1 = strlen(str1);
    	s2 = strlen(str2);
    	s3 = s1+s2+1;
    	a = malloc(s3);
    	for(i = 0; i < s1; i++) {
    		a[i] = str1[i];
    	}
    	for(i = 0; i < s2; i++) {
    		a[i+s1] = str2[i];
    	}
    	a[s3] = '\0';  
    
    	return a;
    }
    
    
    int main(void)
    {
    	printf("%s\n",my_strcat("Hello","world!"));
    	return 0;    
    }