ATM machine program in C

Question

I've coded a basic ATM machine program which contains the features like create an account, check balance, do transactions...etc but it's not completed though. I've used file to store the data and to read it. The read_account fucntion to read, write_account function to create new account and no_of_accounts to get number of accounts in the file all working properly. The problem is with find_account_number which should take an account number as it's parameter and return index at which the account number is.

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

#define MAX_act 100 
typedef struct{
    long account_number;
    int CVV;
    int PIN;
    float balance;
    long phone_number;
} act;

void write_account(long account_number, int CVV, int PIN, long phone_number)
{
    FILE *f;
    act *account = (act*) malloc(sizeof(act));
    f = fopen("account_data", "a");
    *account = (act) { account_number, CVV, PIN, 0, phone_number};
    fprintf(f, "%ld %d %d %.2f %ld\n", account->account_number, account->CVV, account->PIN, account->balance, account->phone_number);
    fclose(f);
}

act* read_accounts(void){
    FILE *f;
    int i = 0;
    f = fopen("account_data", "r");
    act *accounts = (act*) malloc(sizeof(act)*MAX_act);
    while(fscanf(f, "%ld %d %d %f %ld", &accounts[i].account_number, &accounts[i].CVV, &accounts[i].PIN, &accounts[i].balance, &accounts[i].phone_number) == 5){
    i++;
    }
    fclose(f);
    return accounts;
}

int no_of_accounts(void){
    FILE *f;
    int i = 0;
    act *accounts;
    f = fopen("account_data", "r");
    while(fscanf(f, "%ld %d %d %f %ld", &accounts->account_number, &accounts->CVV, &accounts->PIN, &accounts->balance, &accounts->phone_number) == 5)
    i++;
    free(accounts);
    return i;
}

int find_account_no(long account_number, int no_of_accounts, act *accounts){
    int i = 0;
    act *account = accounts;
    printf("yes, it's called\n");
    for(i=0; i< no_of_accounts; i++){
        printf("%ld\n", account[i].account_number);
        if(account[i].account_number == account_number)
        return i;
    }
    return -1;
}


int main(){
    //write_account(123, 111, 222, 939);
    //write_account(321, 111, 222, 939);
    //write_account(123, 111, 222, 939);

    find_account_no(123, no_of_accounts(), read_accounts());
    printf("%d\n", no_of_accounts());
}

so in the function find_account_number I've passed a account number, no 0f accounts and the pointer to an array in which the account data is stored using read_accounts function. Where's the bug? The output is printing not expectedly.

the data in the file is 123 111 321 50.00 939\n 456 222 654 50.00 830\n 789 333 987 0.00 900\n The output is printing as yes, it's called 7503872 456 789 — valli, Apr 18 '23 at 16:35
Please add the information about file contents and the output you are seeing into your question by using [edit]. If the write_account function is not being called, it does not need to be in your question - see also: [mre]. — teapot418, Apr 18 '23 at 16:48
Obligatory: things like account and phone "numbers" aren't really _numbers_ but rather strings of digits, and should be treated as such. — Chris, Apr 18 '23 at 16:54
Aside: some of the variable types are incorrect. PIN, account and phone "numbers" should be strings - they are not integers but happen to be numeric. Balance should be an integer type: please read [Why not use Double or Float to represent currency?](https://stackoverflow.com/questions/3730019/why-not-use-double-or-float-to-represent-currency) Certainly, never use `float` for any purpose at all unless there is a very good reason why you should not use `double` - the inferior `float` cannot even store my salary accurately, or be used for a basic 8-digit calculator. — Weather Vane, Apr 18 '23 at 17:00
@WeatherVane "Balance should be an integer type" -->is far too limiting. Using decimal floating point (expected in C23 as an optional feature) and `double` as cents as well as other approaches are all reasonable. IAC, the account as numbers/strings and money debate are at best a side distraction to OP's fundamental problem: compiling without all warnings enabled. — chux - Reinstate Monica, Apr 18 '23 at 17:17

score 3 · Accepted Answer · answered Apr 18 '23 at 17:11

The problem is with find_account_number which should take an account number as it's parameter and return index at which the account number is.

This function calls no_of_accounts() which does not allocate any memory

int no_of_accounts(void){
    FILE *f;
    int i = 0;
    act *accounts;
    f = fopen("account_data", "r");
    while(fscanf(f, "%ld %d %d %f %ld", &accounts->account_number, &accounts->CVV, &accounts->PIN, &accounts->balance, &accounts->phone_number) == 5)
    i++;
    free(accounts);
    return i;
}

In other functions you do allocate memory. This error would have been revealed if you enable compiler warnings - always essential.

warning C4700: uninitialized local variable 'accounts' used

ATM machine program in C

1 Answers1