#include <stdio.h>
#include <stdlib.h>

void concat(char *p, char *str1, char *str2)
{
	int i,j;

	for (i = 0; str1[i]; i++) {
		p[i] = str1[i];
	}
	for (j = 0; str2[j]; j++) {
		p[i++] = str2[j];
	}
	p[i] = 0;
}

int main(void)
{
	char str1[10] = "hello", str2[10] = "world!!!", *p;

	p = (char *)malloc(sizeof(char) * 20);
		if (p == (char *)NULL) {
			fprintf(stderr, "malloc fail!!!\n");
			exit(1);
		}
	concat(p, str1, str2);
	printf("%s \n", p);
}