I'm trying to apply the do while loop in my c program login but i dont get it

Question

kindly please help me with my problem

#include <stdio.h>
#include <string.h>
int samplepre ()
{
    do {

    char username[3]; // users's input username
    char password[3]; //user's input password
    char choice; // Main menu choice
    char x; // option try again
    char string;
    int i; // for for loop : index

    printf ("\t************\n");
    printf ("\t*Login Menu*\n");
    printf ("\t************\n");

    printf ("Enter your username:"); // The user is ask to input its username
    scanf  ("%s",username);
    printf ("Enter password:"); // The user is ask to input its password
    scanf  ("%s",password);

    if (strcmp(username,"admin") == 0 && strcmp(password,"vdedote") == 0)
    {  // if the condition is true the set of codes will execute
       system ("cls");
       printf ("****************\n");
       printf ("*WELCOME ADMIN!*\n");
       printf ("****************\n");
       system ("PAUSE");
       //printf ("\n");
       printf ("What may I be of service sir?\n");
       printf ("************\n");
       printf ("*MAIN MENU:*\n");
       printf ("************\n");
       //printf ("\n");          
       printf ("[A] Remove Vowels\n"); // The user will be asked of his own choice
       printf ("[B] Remove Entered Character\n");
       printf ("[C] Arithmetic\n");
       printf ("Select your choice:");
       scanf  ("%s",choice);

   }
    else 
    {     // if the user inputs wrong data
         // x = option try again
     printf ("****************\n");
     printf ("*ACCESS DENIED!*\n");
     printf ("****************\n");
     printf ("Would you like to try again <Y/N>");
     scanf  ("%s",x);
    }
    while (strcmp(username,"admin") == 1 && strcmp(password,"vdedote") == 1);
}

Update your question describing where exactly you have difficulties. — Jabberwocky, Nov 06 '15 at 14:09
@iharob i want my program to do a do while loop , for example if the user entered the wrong username and password, i want the program to ask it all over again until it types the correct username and password. — vdedote, Nov 06 '15 at 14:17
The program will most likely crash as it combines `scanf` with an char array of size **3**. Plus there is no check if the strings are null-terminated before they are send to strcmp. — Simon Kraemer, Nov 06 '15 at 14:32
There are to many problems in there, any way you should check scanf for errors. [Try This](http://ideone.com/phRJwF). — Michi, Nov 06 '15 at 17:43

score 2 · Answer 1 · edited May 23 '17 at 12:23

2

You are missing a } before the while.
You need to move username and password out of your loop.
You shouldn't use scanf http://c-faq.com/stdio/scanfprobs.html
You are not allocating enough space for your username and password

Maybe you should read a tutorial about proper reading first? The answer to this question looks pretty nice: how to read string entered by user in c

edited May 23 '17 at 12:23

Community

1
1

answered Nov 06 '15 at 14:11

Simon Kraemer

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i want my program to do a do while loop , for example if the user entered the wrong username and password, i want the program to ask it all over again until it types the correct username and password. – vdedote Nov 06 '15 at 14:19
@vdedote Actually it is pretty clear what you are trying to do. You just made so many errors ... Your idea is correct in most part but the realization is lacking correctness... – Simon Kraemer Nov 06 '15 at 14:34

score 1 · Answer 2 · answered Nov 06 '15 at 14:10

1

You're missing a closing brace } just before the while.

Once you've fixed this syntax error, be sure to understand that strcmp returns zero if the strings are equal.

answered Nov 06 '15 at 14:10

Bathsheba

231,907
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i want my program to do a do while loop , for example if the user entered the wrong username and password, i want the program to ask it all over again until it types the correct username and password. – vdedote Nov 06 '15 at 14:19

score 1 · Answer 3 · edited Nov 06 '15 at 14:11

1

Because you are not closing the do !!

do{.......} 
while(...);

edited Nov 06 '15 at 14:11

Iharob Al Asimi

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answered Nov 06 '15 at 14:11

Mostafa Darwish

91
4

i want my program to do a do while loop , for example if the user entered the wrong username and password, i want the program to ask it all over again until it types the correct username and password. – vdedote Nov 06 '15 at 14:19

hewi · Accepted Answer · 2015-11-06T14:35:34.503

thanks for your question,

After you corrected the syntactical errors (braces)
After you have made the indentation look better
After you have understood the idea of strcmp
After you have understood that doing it this way is VERY dangerous

then and only then:

should you end the do .. while .. loop with a conditional statement where it is checked IF the user is NOT the admin, then you repeat!

    while (strcmp(username,"admin") != 0 && strcmp(password,"vdedote") != 0);

so the loop knows it needs to repeat because it is not the admin with the right password login in!

score 0 · Answer 5 · answered Nov 06 '15 at 14:09

0

The thing is strcmp() returns 0 when the strings are equal.

int strcmp(const char *s1, const char *s2);
RETURN VALUE

The strcmp() and strncmp() functions return an integer less than, equal to, or greater than zero if s1 (or the first n bytes thereof) is found, respectively, to be less than, to match, or be greater than s2.

answered Nov 06 '15 at 14:09

Iharob Al Asimi

52,653
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it expected a 'while' at the end of the input – vdedote Nov 06 '15 at 14:11
and how will the do while loop works in c program – vdedote Nov 06 '15 at 14:11
1

The indentation of your code is bad, it's confusing and one needs to count braces in order to tell whether or not they are correct. – Iharob Al Asimi Nov 06 '15 at 14:12
i want my program to do a do while loop , for example if the user entered the wrong username and password, i want the program to ask it all over again until it types the correct username and password. – vdedote Nov 06 '15 at 14:19
1

The first `strcmp` is correct. Only the second one (in the loop) should use `!=0` instead of `=1` – Simon Kraemer Nov 06 '15 at 14:30

I'm trying to apply the do while loop in my c program login but i dont get it

5 Answers5