char *strsub(char *s,char *pat,char *rep)
{
	char *ptr, *tptr;
	int plen,rlen;
	tptr=ptr=s;
	plen=strlen(pat);
	rlen=strlen(rep);

	if ((ptr=strstr(s,pat))==NULL)
	{
		return NULL;
	}

	tptr = (char*)calloc(strlen(rep) + 1,sizeof(rep[0]));

	if (tptr==NULL)
	return NULL;

	strcpy(tptr,ptr+plen);

	while(rlen--)
	{
		*ptr++=(*(rep++));
	}
	strsub(s,pat,rep);
	free(tptr);
	return (ptr);
}
int main()
{
	char* s={"This is an issue"};
	char* pat={"is"};
	char* rep ={"ere"};
	printf("%s",strsub(s,pat,rep));

	getch();
}