strcat

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

int main (int argc, char **argv){

    char *str;
    char str1[]="First";
    char str2[]=" Second";

    str = malloc(strlen(str1)+1);

    if(!str)
    {
        printf("error: cannot allocate memory block.\n");
        return 1;
    }

    strcpy(str, str1);

    printf("%s\n", str);

    //should be large enough to contain the concatenated resulting string
    char *strTmp = realloc(str,strlen(str1)+strlen(str2)+1);

    if(!strTmp)
    {
        printf("error: cannot reallocate memory block.\n");
        free(str);
        return 1;
    }

    str = strTmp;

    strcat(str, str2);

    printf("%s\n", str);

    free(str);

return 0;
}

/*
First
First Second
*/