A simple program that uses assert() function.

/*
 * main.c
 *
 *  Created on: 15 Mar 2014
 *      Author: Aadit
 */

#include <stdio.h>
#include <string.h>
#include <conio.h>
#define SUCCESS "Operation success!\n"
#include "main.h"
#define USAGE   printf("usage:<program name> command.\n");
struct userbase user1;
#include <assert.h>
int main(int argc,char *argv[])
{
    if(check(argc,argv,&user1) == 2)
    {
        printf(SUCCESS);
    }
    else if(check(argc,argv,&user1) == CHECK_ERROR)
    {
        printf("Command not matched!\n");
    }
    else
        USAGE;

    assert(user1.password != NULL && user1.username != NULL);
    printf("Username =%s\nPassword = %s\n",user1.username,user1.password);
}

/*
 * main.h
 *
 *  Created on: 15 Mar 2014
 *      Author: Aadit
 */

#ifndef MAIN_H_
#define MAIN_H_

struct userbase
{
    char *username;
    char *password;
};

// return 2 if success
#define CHECK_ERROR  4
int check(int a,char *x[],struct userbase *u)
{
    if(a == 2)
    {
        if(!strcmp(x[1],"start"))
        {
            u->username = "aadit";
            u->password = "password";

            return 2;
        }
        return CHECK_ERROR; // 4
    }
    else
        return 1;
}


#endif /* MAIN_H_ */