Thread: Help with creating a program to store student records using string arrays

First I'll post the assignment, then explain my problem, and then post my code.

Assignment:
Instructions:
You are to create a program that tracks student grades.
When the program launches the user should be presented with three options;

Press 0 to exit
Press 1 for author info
Press 2 to Log in

Selecting 0 exits the program
Selecting 1 prints your name and student id
Selecting 3 prompts the user to enter a user name and password.
You should then open the file "passwords" and see if the user is authorized to use the program*
If the username + password was not valid print an error to the user and go back to the previous menu.

*The passwords file will contain a list of user names and passwords, in the format of:
user1 password1
user2 password2
user3 password3

If the username + password was valid present the user with a new menu:
Press 1 for author info
Press 2 to Enter new student
Press 3 to enter grade for existing student
Press 4 to print student records
Press 5 to save student records
Press 6 to load student records
Press 7 to logout

Selecting 0 exits the program
Selecting 1 prints your name and student id
Selecting 2 Prompts the user for a first and last name. Store this information in the system as a student record.
You should be able to handle 1000 students.
Student records have
First name,
Last name,
Student ID,
A list of grades (up to 100 classes). Grades are entered in grade point format (4.0 for an A)

Selecting 3 prompts the user for a student ID and a grade to be entered. Store this grade in that student's record.
Selecting 4 prints the names, ids, GPA and a list of all earned grades for every student. See the sample file for formatting.
Selecting 5 prompts the user for a file name and saves all stored student records to a file. (or in other words, save game)
Selecting 6 prompts the user for a file name and loads student information from a file (or in other words, load game)
Selecting 7 Log out the current user and return to the shorter menu from above.

Your program should also keep a log file of all launch, log in, failed log in, log out, save, load, student creation, grade entry attempts, as well as application exit
This file should be called students.log persist across multiple application starts.
except for exit and start entries, the current logged in username should also be entered in the log.

Note: When loading you can assume all previous student entries are being deleted, rather than detecting repeat students.

Problem:
I began writing the code and am having difficulty with it checking if the entered username and password are similar with the username and password in the file. note that I have a file that has usernames and passwords corresponding to those usernames listed in a format explained in the instructions. If someone can help me start this correctly and throughout this program as i encounter problems that would be awesome.

Code:

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


typedef struct student
{
    char fname[100], lname[100], ID[100];
    double grades;
}student;


int main()
{
    student arr[1000];


    int i = 0;
    int a = 0;
    int sim;
    char username[100];
    char password[100];
    char fusername[100], fpassword[100];




    while (1)
    {


        printf("Press 1 for author info\nPress 2 to Log in\n");


        scanf("%d", &a);


        if (a == 1)
        {
            printf("Timofey Kononets\n2651763\n");
        }


        if (a == 2)
        {
            FILE *file = fopen("passwords.txt", "r");
            printf("Enter a user name and password\n");
            scanf("%s%s", username, password);
        


            while (fscanf(file, "%s%s", fusername, fpassword) != EOF);
            {
                if (strcmp(username, fusername) == 0);
                {
                    if (strcmp(password, fpassword) == 0);
                    {
                        printf("Login successful\n");
                    }
                }
            }


    
            }
        if (a == 0)
        {
            exit(0);
        }


    
    }
    system("pause");
    return (0);
}

Thanks, but is the while loop given the correct statement because its supposed to scan the file and match the previously entered username with the username in the file and the entered password with the password in the file but when i try to run it, it breaks at the loop and i cant seem to figure out what the problem is

Did you remove the semicolons as per Salem's advice?
Post your current code.

Code:

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


typedef struct student
{
    char fname[100], lname[100], ID[100];
    double grades;
}student;


int main()
{
    student arr[1000];


    int i = 0;
    int a = 0;
    int sim;
    char username[100];
    char password[100];
    char fusername[100], fpassword[100];




    while (1)
    {


        printf("Press 1 for author info\nPress 2 to Log in\n");


        scanf("%d", &a);


        if (a == 1)
        {
            printf("Timofey Kononets\n2651763\n");
        }


        if (a == 2)
        {
            FILE *file = fopen("passwords.txt", "r");
            printf("Enter a user name and password\n");
            scanf("%s%s", username, password);
        


            while (fscanf(file, "%s%s", fusername, fpassword) != EOF)
            {    
                if (strcmp(username, fusername) == 0)
                {
                    if (strcmp(password, fpassword) == 0)
                    {
                        printf("Login successful\n");
                    }
                }
            }
        }
        if (a == 0)
        {
            exit(0);
        }


        


    }
    system("pause");
    return (0);
}

And this is what i have in the passwords.txt file that i made. Its formatted where the first word is the username and second word is the password. Ex: Kenny is the username and Lofton is the password. Its supposed to scan this file and then match the entered data to see if it matches whats in the file.

Passwords.txt:
Kenny Lofton
Otto Orf
Einar Diaz
Huong Pham
Hien Pham
Mahdi Mahmoud
Oussama Stiti
Omar Vizquel

It seems to work for me.

Press 1 for author info
Press 2 to Log in
2 <-- is it possible you're forgetting to do this???
Enter a user name and password
Omar Vizquel
Login successful <-- SUCCESS!
Press 1 for author info
Press 2 to Log in

Usually we would have a separate Username and Password prompt.
You should check that the password file opened properly.
You should close the password file.
You should use a if/else if structure or a switch statement:

Code:

if (a == 0) {
    ...
}
else if (a == 1) {
    ...
}
else if (a == 2) {
    ...
}
else {
    ...
}

// or use a switch

switch (a) {
case 0:
    ...
    break;   // don't forget the break statements!
case 1:
    ...
    break;
case 2:
    ...
    break;
default:
    ...
    break;   // doesn't really need a break since it's the last one
}

This is what i get when i enter the username and password

It looks like your passwords file is not opening properly, hence my advice to check it:

Code:

FILE *file = fopen("passwords.txt", "r");
if (file == NULL) {
    perror("passwords.txt");
    exit(EXIT_FAILURE);     // remember to include <stdlib.h>
}
...
// and remember to
fclose(file);

The password file is probably in the wrong directory. I don't know where it should go, but you could try it in different places in the project directory.

Are you on windows? Hiding file extensions? Have you accidentally called your file passwords.txt.txt in which case the fopen will fail which is signified by fopen returning a NULL pointer ?

Yes I'm on windows. That could be it because after i input the if statement that algorithm gave me, it doesn't even pull up the program, every time i try to run it on visual studio it doesn't even pull up the command prompt. So should i make another file?

Also, I'm wondering how should i code if someone enters an invalid username or password for it to say login unsuccessful

the passwords file is a txt document so isn't that why the .txt extension is put so that it reads from the txt file?

call up file explorer, check the view menu and make sure the box show file extensions is ticked. Then check your passwords file is 1) where it is supposed to be ( same directory as the built executable) and 2) that it is actually called passwords.txt and not miscalled passwords.txt.txt

Your last code posted works, you have a problem with a misnamed file, a misplaced file, or file permissions.

I'm having trouble inputting the student ID. The way its supposed to work is that the ID is supposed to correlate with each index, meaning if each index is a student, then the ID is equivalent to the order in which each student is inputted. So index 0 is ID 0 and student index 85 is ID 85. I'm also wondering how would it be correct to print the info according to choice 4.

Here is a sample of how things are supposed to work as given by my teacher:
Press 1 for author info
Press 2 to login
2
Enter user name
Kenny
Enter password
Lofton
Login Successful
Press 0 to exit
Press 1 for author info
Press 2 to Enter new student
Press 3 to enter grade for existing student
Press 4 to print student records
Press 5 to save student records
Press 6 to load student records
Press 7 to logout
2
Enter student first name
tim
Enter student last name
kon
Press 0 to exit
Press 1 for author info
Press 2 to Enter new student
Press 3 to enter grade for existing student
Press 4 to print student records
Press 5 to save student records
Press 6 to load student records
Press 7 to logout
3
Enter student ID
0
Enter the numeric value of the grade point for this class
t
5.4
Press 0 to exit
Press 1 for author info
Press 2 to Enter new student
Press 3 to enter grade for existing student
Press 4 to print student records
Press 5 to save student records
Press 6 to load student records
Press 7 to logout
3
Enter student ID
0
Enter the numeric value of the grade point for this class
t
4.2
Press 0 to exit
Press 1 for author info
Press 2 to Enter new student
Press 3 to enter grade for existing student
Press 4 to print student records
Press 5 to save student records
Press 6 to load student records
Press 7 to logout
4
First Name: tim Last Name: kon: GPA: 4.800000
5.400000
4.200000
Press 0 to exit
Press 1 for author info
Press 2 to Enter new student
Press 3 to enter grade for existing student
Press 4 to print student records
Press 5 to save student records
Press 6 to load student records
Press 7 to logout

Here is my code so far:

Code:

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


typedef struct student
{
	char fname[100], lname[100];
	double grades[100];
	int ID;
}student;


int main()
{
	student arr[1000];


	int j = 0;
	int i = 0;
	int a = 0;
	char username[100];
	char password[100];
	char fusername[100], fpassword[100];




	while (1)
	{


		printf("Press 1 for author info\nPress 2 to Log in\n");
		scanf("%d", &a);


		if (a == 1)
		{
			printf("Timofey Kononets\n2651763\n");
		}


		if (a == 2)
		{
			FILE *file = fopen("passwords1.txt", "r");
			printf("Enter a user name\n");
			scanf("%s", username);
			printf("Enter password\n");
			scanf("%s", password);


			while (fscanf(file, "%s%s", fusername, fpassword) != EOF)
			{
				if (strcmp(username, fusername) == 0)
				{
					if (strcmp(password, fpassword) == 0)
					{
						printf("Login successful\n");
					}
					else
					{
						printf("Login unsuccessful\n");
					}
				}
			}
		
		fclose(file);
		}
		while (2)
		{
			
			printf("Press 1 for author info\nPress 2 to enter new student\nPress 3 to enter grade for existing student\nPress 4 to print student records\nPress 5 to save student records\nPress 6 to load student records\nPress 7 to logout\n");
			scanf("%d", &a);


			if (a == 1)
			{
				printf("Timofey Kononets\n2651763\n");
			}
			else if (a == 2)
			{
				printf("Enter student first name\n");
				scanf("%s", arr[i].fname);
				printf("Enter student last name\n");
				scanf("%s", arr[i].lname);
				i++;
			}
			else if (a == 3)
			{
				printf("Enter student ID\n");
				scanf("%d", arr[j].ID);
				printf("Enter a numeric value for the gradepoint in this class\n");
				scanf("%lf", arr[j].grades);
			}
			else if (a == 4)
			{
				for (int k = 0; k < i; k++)
				{
					printf("First name: %s   Last Name: %s   GPA: %lf\n", arr[k].fname, arr[k].lname, arr[k].grades);
				}
				}
		}
		
		if (a == 0)
		{
			exit(0);
		}






	}
	system("pause");
	return (0);
}

You should start by reorganising your code into logical units, functions, rather than having one huge monolithic main function. Solve each problem in its own function and use main to tie it all together.
You are still not checking that fopen hasn't returned a null pointer. That is a must. Don't forget error checking.
Clean up what you already have, then we'll go from there.
while(2) is a little weird. It'll work fine as true is any non-zero number but while(1) is kind of a convention for an infinite loop. system("PAUSE") is just horrible. You can run your code in a debugger and stick a breakpoint on the return 0 line to hold the program open to see output. Get used to using your debugger, it will become a trusted friend over time.