problem logging back in

hi, im fairly new to programming, could any one help me with this:

Code:

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

char set_user[20];
char set_pass[20];
char user[20];
char pass[20];
char old_pass[20];
char new_pass[20];
char old_user[20];
char new_user[20];
char menu_choice[20];
char option_choice[20];
int strcmp( const char *str1, const char *str2 );
void print_options() {
        printf("________________________________________\n");
        printf("TYPE 'user' TO CHANGE YOUR USERNAME\n");
        printf("TYPE 'pass' TO CHANGE YOUR PASSWORD\n");
        printf("TYPE 'logout' TO LOGOUT\n");
        printf("TYPE 'options' TO PRINT OPTIONS\n");
        printf("________________________________________\n");
}
void change_pass(char *str1, char *str2, char *str3) {
        printf("Old Password: ");
        scanf("%s", str1);
        printf("New Password: ");
        scanf("%s", str2);
        if (strcmp (str1, str3) == 0 ) {
                str3 = str2;
                printf("YOUR PASSWORD HAS NOW CHANGED\n");
        }
        else {
                printf("INCORRECT OLD PASSWORD\n");
        }
}
void change_user(char *str1, char *str2, char *str3) {
        printf("Old Username: ");
        scanf("%s", str1);
        printf("New Username: ");
        scanf("%s", str2);
        if (strcmp (str1, str3) == 0 ) {
                str3 = str2;
                printf("YOUR USERNAME HAS NOW CHANGED FROM %s TO %s\n", str1, str2);
        }
        else {
                printf("INCORRECT OLD USERNAME\n");
        }
}
void print_first_options() {
        printf("\n");
        printf("MENU OPTIONS\n");
        printf("_______________________________\n");
        printf("TYPE 'register' TO REGISTER\n");
        printf("TYPE 'login' TO LOGIN\n");
        printf("TYPE 'users' TO SHOW USERS\n");
        printf("TYPE 'options' TO PRINT OPTIONS\n");
        printf("_______________________________\n");
}       

main() {
        int a = 3;
        int b = 3;
        printf("\n");
        printf("WELCOME\n");
        printf("\n");
        while ((a, b) == 3 ) {
                print_first_options();
                printf("Menu choice: ");
                scanf("%s", menu_choice);
                if (strcmp (menu_choice, "register") == 0 ) {
                        printf("REGISTER\n");
                        printf("SET YOUR USERNAME\n");
                        printf("Username: ");
                        scanf("%s", set_user);
                        printf("SET YOUR PASSWORD\n");
                        printf("Password: ");
                        scanf("%s", set_pass);
                        printf("\n");
                        printf("YOURE NOW REGISTERED\n");
                }
                else if (strcmp (menu_choice, "login") == 0 ) {
                        printf("Username: ");
                        scanf("%s", user);
                        printf("Password: ");
                        scanf("%s", pass);
                        if (strcmp (user, set_user) != 0 || strcmp (pass, set_pass) != 0 ) {
                                printf("\n");
                                printf("USERNAME OR PASSWORD IS INCORRECT\n");
                                printf("YOU MAY NEED TO REGISTER\n");
                                printf("\n");
                        }
                        else {
                                while (strcmp (option_choice, "logout") != 0 ) {
                                        printf("\n");
                                        printf("WELCOME TO YOUR SYSTEM %s\n", user);
                                        printf("\n");
                                        print_options();
                                        printf("Option choice: ");
                                        scanf("%s", option_choice);
                                        if (strcmp (option_choice, "options") == 0 ) {
                                                print_options();
                                        }
                                        else if (strcmp (option_choice, "user") == 0 ) {
                                                printf("\n");
                                                printf("CURRENT USERNAME: %s\n", set_user);
                                                printf("\n");
                                                change_user(old_user, new_user, set_user);
                                        }
                                        else if (strcmp (option_choice, "pass") == 0 ) {
                                                printf("\n");
                                                printf("CURRENT PASSWORD: %s\n", set_pass);
                                                printf("\n");
                                                change_pass(old_pass, new_pass, set_pass);
                                        }
                                        else {
                                                printf("\n");
                                                printf("INCORRECT INPUT\n");
                                                printf("\n");
                                        }
                                }
                                printf("\n");
                                printf("YOUVE NOW LOGGED OUT\n");
                                printf("\n");
                        }
                }
        }

---

the problem is when i register and login its fine but when i logout then login again it logs out straight away because the option_choice variables value is always "logout", ive tried declaring option_ choice to a different value after the while option_choice is not equal to "logout" loop but it comes up with a error when i compile it.
Thanks.

Code:

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while ((a, b) == 3 )

---

not what you think it should do.

nonoob, i don't understand??

It's barely legal C... What are you trying to compare? Currently, a is ignored, and b is compared with 3.

ive put a loop around the whole program with while a and b is equal to the number 3
what do you mean by "barely legal C"?

You should write while (a ==3 && b == 3).
You can not compare a set of values separated by commas. In C, the == is not commutative over comma separated statements.

Anyway, I haven't checked the rest of your code. This one is just the obvious syntax problem that jumped out.

So what he's saying is that (a, b) == 3 is technically legal in C (i.e. it is grammatically correct), but not a construct anybody would use. Here is how it's evaluated:
1. Look at the innermost parentheses. Evaluate statements (separated by commas) from left to right.
2. The statement 'a' does nothing, but has a value of a.
3. Then, the statement 'b' is evaluated. It also does nothing, but has a value of b.
4. The parenthetical is given the value of the last statement, b:
5. This value (b) is compared against 3.

Notice that a is never compared to 3. What you need to do is separate these things out and compare them individually, then act accordingly if both a and b are 3:

Code:

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while (a == 3 && b == 3)

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kk, thanks i understand now, but can you help me with the option_choice variable please??

Quote:

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Originally Posted by cprog12

ive tried declaring option_ choice to a different value after the while option_choice is not equal to "logout" loop but it comes up with a error when i compile it.

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By declaring do you mean assigning it a different value? If so, how are you "assigning" it? I don't see that code in your post. It's worth noting that you can't simply assign strings in C the way you can an int, float, char. etc. You have to use strcpy. An alternative, that would simply make option_choice appear empty is to do option_choice[0] = '\0'. That makes the first character the null character, so there is no data in the string, just an "end of string" marker.

You are comparing option_choice before having initialized it.

yes i mean assigning it, and ive tried this, i know it might look stupid but im new to C:

Code:

---

main() {
        int a = 3;
        int b = 3;
        printf("\n");
        printf("WELCOME\n");
        printf("\n");
        while (a == 3 && b ==3) {
                char option_choice = NULL;
                print_first_options();
                printf("Menu choice: ");
                scanf("%s", menu_choice);
                if (strcmp (menu_choice, "register") == 0 ) {

---

Code:

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char option_choice = NULL;

---

to try and change the value of the option_choice so that when i next login the value wont be "logout", which is causing it to logout straight away.

ive initialized it as a global variable, should it be local???

Not necessarily. Just intitialize it to null string right inside your main while loop.

Code:

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option_choice[0] = '\0';

---

it works, thanks for that nonoob and the other guy

Woohoo! And thanks anduril462 for clarifying comma separated statements. I use them so rarely ... only in for statements to do multiple initializations.