I have just finished a simple C program which is basicaly composed of 3 functions:

• accadd(void){} which adds some customer details to a binary file
• void view(char file[30]){} which is supposed to let me view some of the data in a .txt file
• void modify(char file[30]){} which verifies if a value of a struct is present in the binary file. If that value exists, it will replace it with the newly inserted one.

Now, I'm pretty new to C (coming from python world - should've learnt them in the opposite order ^__^) and I am sure that there are better ways of improving what I have just written. So I am looking for some advices / tips / improvements in my way of thinking + optimization of the code.

Here is the program:

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

void menu(void);
void accadd(void);
void modify(char file[30]); 
void view(char file[30]);

// this should remain as it is
struct date
{
    int day;
    int month;
    int year;
};

// this should also remain as it is
struct customer
{
    char name[40], acctype[10];
    int accno, age;
    double phone;
    float amount;
    struct date deposit;
} add;

void accadd(void)
{
    FILE *fp = fopen("cus.dat", "ab+"); // open the binary file

    if (fp == NULL) // making sure that the file is ok
        exit(1);
    
    // start adding data
    printf("ADD RECORD\n");
    printf("Enter today's date(date/month/year) \n");
    if (scanf("%d/%d/%d", &add.deposit.day, &add.deposit.month, &add.deposit.year) != 3)
        exit(1);

    printf("Enter account number\n");
    if (scanf("%d", &add.accno) != 1)
        exit(1);

    printf("Enter customer's name\n");
    if (scanf("%s", add.name) != 1)
        exit(1);

    printf("Enter customer's age\n");
    if (scanf("%d", &add.age) != 1)
        exit(1);

    printf("Enter customer's phone num\n");
    if (scanf("%lf", &add.phone) != 1)
        exit(1);

    printf("Enter the account type(in words): \n\t 1:Current\n\t 2:Saving\n\t 3:Fixed\n");
    if (scanf("%s", add.acctype) != 1)
        exit(1);

    printf("Almost done! Just enter the amount you want to deposit: ");
    if (scanf("%f", &add.amount) != 1)
        exit(1);

    //add data to the binary file
    fwrite(&add, sizeof(add), 1, fp);
    fclose(fp);
}

// this is pretty straight-forward so I didn't add any comments on it
void view(char file[30])
{
    FILE *view, *output;
    int test = 0;
    output=fopen("output.txt", "w");
    fprintf(output,"Customer's List\n");
    fprintf(output,"\tCustomer's Name:");
    fprintf(output,"\tAccount Number:");
    fprintf(output,"\tCustomer's Phone No:\n");
    view = fopen(file, "rb");

    if (view == NULL)
        exit(1);

    while (fread(&add, sizeof(add), 1, view) != 0)
    {
        fprintf(output,"\t%16s", add.name);
        fprintf(output,"\t%15d", add.accno);
        fprintf(output,"\t%20.0f", add.phone);
        fprintf(output,"\n");
        test++;
    }
    fclose(view);
    fclose(output);

    if (test == 0)
    {
        printf("NO RECORDS FOUND!\n");
    }
    else{
        printf("Output updated in file output.txt\n");
    }
}

void modify(char file[30]){
    FILE *view;
    int counter = 0;

    view = fopen(file, "rb+");

    if (view == NULL)
        exit(1);

    while (fread(&add, sizeof(add), 1, view) != 0)
    {
        if(add.phone==777777777){
            printf("Old phone is: %f",add.phone);
            printf("Enter the new phone: ");
            scanf("%f", &add.phone);
            printf("\nThe new phone is: %f",add.phone);
            fseek(view,sizeof(add)*counter,SEEK_SET);
            fwrite(&add,sizeof(add),1,view);
        }
            counter++;
    }
    fclose(view);

    if (counter == 0)
    {
        printf("NO RECORDS FOUND!\n");

    }
    else{
        printf("add.phone printed: %i\n",counter);
        printf("add length %d\n",sizeof(add));
    }
}


void menu(void)
{
    int n,account_number;
    char file[30],account_name[30];
    printf("Enter your choice 1, 2, 3\n");
    printf("\n1. Insert new data about the customer");
    printf("\n2. Output data in output.txt file");
    printf("\n3. Modify phone nr.");
    printf("\n\nYour choice(1, 2, or 3): ");
    while(1){

        if (scanf("%d", &n) != 1)
            exit(1);

        switch (n){
        case 1:
            accadd();
            break;
        case 2:
            printf("Enter the file name: ");
            scanf("%s",&account_name);
            view(account_name);
            break;
        case 3:
            modify("cus.dat");
            break;
        }
        printf("Enter your choice 1, 2, 3\n");
        printf("\n1. Insert new data about the customer");
        printf("\n2. Output data in output.txt file");
        printf("\n3. Modify phone nr.");
        printf("\n\nYour choice(1, 2, or 3): ");

    }
}

int main(void)
{
    menu();
    return 0;
}