What is wong with my code

Question

I'm a C++ programmer, so get lost on IO and strings in C, so please forgive my ignorance.

This program fails on the fclose statement. It says the file does not exist.  If that is the case, I'd expect it to fail on the open or the fprintf.

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

int main()
{
    FILE *fptr;
    char contact[100], contact1[100];
    printf("Enter first name, last Name, phone number\n");
    gets(contact);
    fopen("ContactList.txt","w");
     fprintf(fptr,"%s  %c",contact, '\n');
   fclose(fptr);
     fopen("ContactList.txt","r");
     fscanf(fptr,"%d", "%s %s %s ",contact1);

    printf("%s %s %s %c",contact1, '\n');
    return 0;
}

Answer 1

There are many problems with your code.

First of all, fopen returns the pointer of the opened file, which you do not store in fptr (which remains to store a random memory address).

Second, scanf and printf argument count did not match the format string.

I've fixed your code below:

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

int main()
{
    char contact[100];
    printf("Enter first name, last Name, phone number\n");
    fgets(contact, sizeof(contact), stdin);
    FILE * fptr = fopen("ContactList.txt", "w");
    if (!fptr)
    {
        printf("Failed to create file.\n");
        return -1;
    }
    
    fprintf(fptr, "%s\n", contact);
    fclose(fptr);

    fptr = fopen("ContactList.txt", "r");
    if (!fptr)
    {
        printf("Failed to open file.\n");
        return -2;
    }
    char firstName[100];
    char lastName[100];
    char phoneNumber[100];
    fscanf(fptr, "%s %s %s", firstName, lastName, phoneNumber);
    printf("First name: %s\n", firstName);
    printf("Last name: %s\n", lastName);
    printf("Phone Number: %s\n", phoneNumber);
    return 0;
}

Answer 2

You have not assigned file location to your pointer *fptr.
Try,

fptr = fopen("ContactList.txt","w");