reading values into struct of arrays

Question

I need to create an array of struct with the struct being a student (with data types string FirstName, string LastName, int testScore, and char Grade). I have the logic figured out for the function prototypes, and I have learned a little bit of basic file i/o. I want 20 students in the array of structs, and the info is to be read in from .txt files. This is where I am having trouble. Here is my basic code.

#include "stdafx.h"
#include <iostream>
#include <fstream>
using namespace std; 

struct studentType {
   string firstName;
   string lastName; 
   int testScore; 
   char Grade; 
};

int main()
{
   studentType students[20];

   int i;

   ifstream inputFile; 
   inputFile.open("testScores.txt"); 

   for (i = 0; i < 20; i++)
      inputFile >> students->testScore; 

   cout << "The test scores entered are: "; 

   for (i = 0; i < 20; i++)
      cout << " " << students->testScore; 

   return 0;
}

I also added a reference file "testScore.txt." When I output I get the first value from the text file 20 times. Is this taking the first value of testScore.txt and storing into all the testScore members of studentType? — Drizzt Do'Urden
– Drizzt Do'Urden, Commented Feb 9, 2018 at 21:44
Have you stepped through this in your debugger? What's the actual issue here? On what line does it behave unexpectedly? — MrEricSir
– MrEricSir, Commented Feb 9, 2018 at 21:45

Arnav Borborah · Accepted Answer · 2018-02-09 21:50:47Z

2

You forget to index the element from the array when you access the array. Change:

students->testScore

To:

students[i].testScore

In both loops. The first version only does the changes to the first element (Since it can be accessed with *students), while the second adds the index to the pointer.

This is just another good reason to use std::vector or std::array since if you tried to dereference them as you did with the array here, you would get an obvious error.

On a side note, in C++, you should declare your loop variables inside your loops. Declaring them outside is something that used to be necessary before C99, but not C++.

edited Feb 9, 2018 at 21:50

answered Feb 9, 2018 at 21:46

Arnav Borborah

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3 Comments

Drizzt Do'Urden Over a year ago

Oh, so I just added the value of the first line of .txt to the first element of the array member then printed it 20 times... :P lol thank you though it worked.On the side note, c++ doesn't use curly braces for loops? I'm guessing I should just declare the loop variable under the if statement?

Arnav Borborah Over a year ago

@DrizztDo'Urden Yes, you are correct in what happened with your code. With the loop, I meant you should replace int i; for (i = 0; i < x; ++i) {} with for(int i = 0; i < x; ++i) {}. The latter limits the scope of the variable to a small area. Also, if you found this answer helpful, please consider accepting it by clicking the checkmark below the downvote button.

Drizzt Do'Urden Over a year ago

Ah so put the variable declaration in the loop parameters. Got it.

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