An Bank application made for my project in C Programming in KKU

bank.c

/* 
    Fully Devolped by Yazeed Alahmad and Mohmammad Alasmari
*/

// These are the libraries that used in this project
#include <stdlib.h>
#include <string.h>
// These libraries are only for some text formatting purposes
    #include <stdio.h>
    #include <windows.h>

// Global Variables Section #

    // This variable is for selecting the loggedin user
    int selectedUsername = -1;

    // The example database arrays
    // 10 -> max users ~~ 30 -> max letters per string
    char usernames[10][30] = {
        "Ahmad",
        "Yazeed",
        "Mohammad"
    };
    char passwords[10][30] = {
        "1234",
        "0000",
        "1122"
    };
    double balances[10]  = {
        0.0,
        100.0, 
        122.0
    };

    // These arrays are for storing history and saves the actions
    char historyActionTypes[10][100][20];   // History array for action name
    double historyAmounts[10][100];     // History array for action amount
    int historyCount[10] = {0};     // Number of actions for each user


// This functions is to login and validate the username and password
void loginPage() {
    char username[30];
    char password[30];

    system("cls");
    printf("\nEnter your -USERNAME- : ");
    gets(username);
    printf("\nEnter your -PASSWORD- : ");
    gets(password);

    int logged = 0;

    for(int i = 0; i < 10; i++) {
        if (strcmp(username, usernames[i]) == 0) {
            if (strcmp(password, passwords[i]) == 0) {
                selectedUsername = i;
                logged = 1;
            }
        }
    }

    if(logged == 0) {
        loginPage(); // recursion
    }
}

void logoutPage() {
    selectedUsername = -1;
    system("cls");
    printf("You have been logged out.\n");
    Sleep(2000);
}


// Micro functions #
    // This function is to add an action to the history array
    void addToHistory(const char *actionType, double amount) {
        // Check if he is loggedin and history count is not too much over 100 action
        if (selectedUsername != -1 && historyCount[selectedUsername] < 100) {
            // Copy the action type to the array
            strcpy(historyActionTypes[selectedUsername][historyCount[selectedUsername]], actionType);
            // Copy the action amount to the array
            historyAmounts[selectedUsername][historyCount[selectedUsername]] = amount;
            // Adding 1 to the history to make sure he is still in the range of 100
            historyCount[selectedUsername]++;
        }
    }

    // This function is to change the username by getting a pointer parameter
    void changeUsername(char *newUsername) {
        // Check if the new username already exists
        for (int i = 0; i < 10; i++) {
            if (i != selectedUsername && strcmp(newUsername, usernames[i]) == 0) {
                printf("Username already exists! Please choose a different username\n");
                Sleep(2000);
                return;
            }
        }

        // Update the username using pointers
        strcpy(usernames[selectedUsername], newUsername);

        printf("Username changed successfully\n");
        addToHistory("Username changed", -1);
        Sleep(2000);
    }

    // This function is to change the password by getting a pointer parameter
    void changePassword(char *newPassword) {
        // Update the password using pointers
        strcpy(passwords[selectedUsername], newPassword);

        printf("Password changed successfully\n");
        addToHistory("Password changed", -1);
        Sleep(2000);
    }


// Actions Functions #
    // This function is for deposting ( adding ) amounts to the account balance
    void depositePage() {
        system("cls");
        printf("- Deposite Balance\n\nPlease enter the amount in $");
        int amount;
        scanf("%d", &amount);
        balances[selectedUsername] = balances[selectedUsername] + amount;
        addToHistory("Deposit", amount);
    }

    // This function is for withdrawl ( removing ) amounts from the account balance
    void withdrawPage() {
        system("cls");
        printf("- Withdraw Balance\n\nPlease enter the amount in $");
        int amount;
        scanf("%d", &amount);
        balances[selectedUsername] = balances[selectedUsername] - amount;
        addToHistory("Withdrawal", amount);
    }

    // This function is for transfering amounts between the saved acccounts by subtracting the amount from the logged user and adding it to the desired user
    void transferPage() {
        system("cls");
        printf("- Transfer Balance\n\nPlease enter the Recipient username: ");

        char recipientName[30];
        int recipientID = -1;

        scanf("%s", recipientName);

        // Find the recipient ID
        for (int i = 0; i < 10; i++) {
            if (strcmp(recipientName, usernames[i]) == 0) {
                recipientID = i;
                break;
            }
        }

        if (recipientID != -1) {
            printf("\nPlease enter the amount in $");
            double amount;
            if (scanf("%lf", &amount) != 1 || amount <= 0) {
                // Invalid amount
                printf("\nInvalid amount.\n");
                Sleep(2000);
                return;
            }

            if (amount <= balances[selectedUsername]) {
                balances[selectedUsername] -= amount;  // withdrawing the amount from the logged user
                balances[recipientID] += amount;       // depositing the amount to the desired user
                printf("\n\nTransfer successful\n");
                addToHistory("Transfer", amount);
                Sleep(2000);
            } else {
                printf("\nYour balance is not enough to transfer\n");
                Sleep(2000);
            }
        } else {
            printf("\nRecipient not found\n");
            Sleep(2000);
        }
    }

    // This function is to show multiple actions to do and call these functions alone
    void accountSettingsPage() {
        system("cls");

        printf("Account Settings\n");
        printf("=======================\n");
        printf("1) Change Username\n2) Change Password\n3) Back to Main Menu\n");
        printf("=======================\n");

        int choice;
        scanf("%d", &choice);

        char newInput[30];

        switch (choice) {
            case 1:
                printf("Enter your new username: ");
                scanf("%s", newInput);
                changeUsername(newInput);
                accountSettingsPage();
                break;
            case 2:
                printf("Enter your new password: ");
                scanf("%s", newInput);
                changePassword(newInput);
                accountSettingsPage();
                break;
            case 3:
                // Back to the main menu
                break;
            default:
                printf("Invalid choice! Please try again\n");
                Sleep(2000);
                accountSettingsPage();
        }
    }

    // This function is to show the account logging details and balance with a brief history of the actions he did
    void bankstatementPage() {
        system("cls");
        printf("- Bank Details & History\n");
        printf("=======================\n");
        printf("Your USERNAME is : %s\n", usernames[selectedUsername]);
        printf("Your PASSWORD is : %s\n", passwords[selectedUsername]);
        printf("=======================\n");
        printf("Your Available Balance is : $%.2lf\n", balances[selectedUsername]);
        printf("=======================\n");

        printf("Transaction History:\n");
        for (int i = 0; i < historyCount[selectedUsername]; i++) {
            if(historyAmounts[selectedUsername][i] == -1){
                printf("%s\n", historyActionTypes[selectedUsername][i]);
            }else {
                printf("%s: $%.2lf\n", historyActionTypes[selectedUsername][i], historyAmounts[selectedUsername][i]);
            }
        }
        printf("\n=======================\n");

        printf("Press ( 1 ) To back to main menu\n");

        int i;
        scanf("%d", &i);
    }



void main() {
    // System("cls") is used to make the app look as a multi page actions this command helped us alot to make it looks good!
    system("cls");

    // to make sure the user name is logged in which :
    // -1 means that he is not logged in with any user
    if(selectedUsername != -1) {
        system("cls");

        // Welcome headline and balance
        printf("Welcome %s to KKU Bank!\n", usernames[selectedUsername]);
        printf("$%.2lf\n\n", balances[selectedUsername]);
        // Main menu options
        printf("Please Enter your choice number\n");
        printf("=======================\n");
        printf("1 -) Deposit Balance\n2 -) Withdraw Balance\n3 -) Transfer Balance\n4 -) Bank Details & History\n5 -) Account Settings\n6 -) Logout\n");
        printf("=======================\n");

        // Enter his choice and read it to check it by switch statement
        int choice;
        scanf("%d", &choice);

        switch (choice)
        {
            case 1:
                depositePage();
                main();
                break;
            case 2:
                withdrawPage();
                main();
                break;

            case 3:
                transferPage();
                main();
                break;

            case 4:
                bankstatementPage();
                main();
                break;

            case 5:
                accountSettingsPage();
                main();
                break;

            case 6:
                logoutPage();
                main();
            default:
                main();
                break;
        }
    }
    else {
        // if the user is not logged in then bring him back to login page
        loginPage();
        main();
    }
}