#include<stdio.h>

int cntChars(char *);
char * concat(char *, char *);

int main(int argc, char **argv)
{
	char *ptrString;
	printf("%s\n", ptrString = concat(*(argv + 1), *(argv + 2)));
	free(ptrString);
	return 0;
}

int cntChars(char *inputString)
{
	// returned value "count" does not include '\0'
	int count = 0;
	while(*(inputString + count) != '\0') ++count;
	return(count);
}

char * concat(char *s1, char *s2)
{
	char *r = NULL;
	int count = 0;
	int countTotal = 0;
	int i;
	int j = 0;

	count = cntChars(s1);
	countTotal = count + cntChars(s2);
	if(!(r = (char *) malloc(sizeof(char) * (countTotal + 1))))
	{
		fprintf(stderr,"Insufficient memory");
		exit(1);
	}
	else
	{
		for(i = 0 ; i < count; i++) *(r + i) = *(s1 + i);
		while(i < countTotal)
		{
			*(r + i) = *(s2 + j);
			j++;
			i++;
		}
		*(r + countTotal) = '\0';
		return r;
	}
}