Performing calculations on loaded arrays

[eazye]

Hello everyone,

I've recently started a programming course and for my first assignment, I was asked to produce a code that would be able to extract up to 100 (1-100) integers from a text file and then give the sum, mean and standard deviation.

My first instinct was to separate the task into two parts: first, I wrote the code for loading the integers into a 1D array. Second, I used a hardcoded array to develop the necessary equations for sum, mean and standard deviation. However, when I combine the two parts, two problems arise:
1)
When I substitute the hardcoded array for the one filled with data from file, the program gives the wrong answers. Upon inspection, I noticed that the array used for sum/mean/sd calculations is nothing like the one loaded from file (which loads successfully), its full of 0s but also some incredibly large numbers.
2)
For some reason, when I have two identical projects open, the break command on eof (line 29) only works in one - when I print the array for the other project, I still get two 100s as my penultimate and final integers.

Any hints or comments would be greatly appreciated!

  
#include <stdio.h>
#include <iomanip>
#include <iostream>
#include <string>
#include <sstream>
#include <fstream>
#include <cmath>

using namespace std; //tells computer to use a particular library of C++ commands

int main()

{
    float sum, mean = 0.0;
    float var, dev, sd, sdev = 0.0;
    int i,n = 0;
    int Array [100];
    
    ifstream integers;
    integers.open("StatNum.txt");
    
    if(!integers) cout << "Error opening file.\n";
    
    while (!integers.eof())
    {
        integers >> Array[i];
        cout << Array[i] <<endl;
        if(integers.eof() ) break; //prevents from reading the last line again
    }
    
    integers.close();
    
    for (n=0; n<100; n++)  //loop the array to get sum and mean
    {
        sum += Array[n];
        
        mean = sum/(n+1);
    }
    
    for(n = 0; n < 100; n++) //std dev loop
    {
        dev = (Array[n] - mean)*(Array[n] - mean);
        sdev = sdev + dev;
    }
    
    var = sdev / (n - 1);
    sd = sqrt(var);
    
    cout <<endl << setprecision(2)<<fixed<< "The sum of " << n << " integers is: " << sum << endl;   //output
    
    cout << "The average of " << n << " integers is: " << mean <<endl;
    
    cout << "The standard deviation of " << n << " integers is: " <<sd << endl;
    
    system("pause"); //on windows it might exit immediately
    
    
    return(0);
    
}

[MiiNiPaa]

1) Do not loop on EOF. YOur attempt to avoid probles is actually useless, as next statement is loop conditon which does the same.

2) Where exactly you store values in array? What is te value of i?

3) for (n=0; n<100; n++) What if there is less numbers? Your code will read garbage which was never initialized.

[eazye]

1) so should I be looking to change the eof part or use something else instead of a loop? I'm still struggling with how while and do while loops work but is this the correct place to use one?

2) From my understanding, i designates the nth cell of the array. Im not sure what you mean by where I store the values in the array.

3) I've also noticed this - should I be looking again into using while loops instead? The only problem I have with that is that I don't know how to declare the array size since it will be dependent on the amount of integers, and I can't find much (or something reasonably written) on dynamic arrays in c++.

[MiiNiPaa]

1) Canonical way to read unknown number of inputs is to loop on input operation:

int x;
while(input >> x) {
    //Use x
}

2) i designates the nth cell of the array But what value does i has? Is it 1, 2 or something else? Which part of your code ensures that? (It is not initialized and never changed in your loop, so all values are written in one, potentially out of bounds, cell)

3) Store how many values were actually read in a variable. Use it as loop sentiel. Alternatively, use a vector, it knows own size and is generally safer and easier to use.

[eazye]

Hey thanks, I ended up using a vector and it turned out much simpler, quicker and elegant!