CODEWITHSUNDEEP
c++arrays
JustMatter
JustMatter

Reputation: 13

Trouble with dynamic arrays and finding the sum of values

So as I explained in the title i'm having trouble trying to get the sum of an array. I've just now learned how to create dynamic arrays and I did some searching on how to calculate the sum. I don't believe I fully understand what is going on to calculate the sum.

// Final Grade Calculator

#include <cstdlib>

#include <iostream>

#include <cmath>

#include <string>

using namespace std;

int main(){
    double minor, quiz, major;
    int minorG, quizG, majorG;

    minorG = 0;

    cout << "Final Grade Calculator" << endl;

    cout << "Input minor grade weight percent." << endl;
    cin >>minor;

    cout << "Input quiz grade weight percent." << endl;
    cin >>quiz;

    cout << "Input major grade weight percent." << endl;
    cin >>major;

    // Three grade categories
    minor = minor/100;
    quiz = quiz/100;
    major = major/100;


    for(int i = 1; i <=10; i++){
        cout << "Input a minor grade. (Max=10)" << endl;
        cin >>minorG;


        int *minorGA = new int[minorG];

        minorG+= minorGA[minorG];
        cout << "Currently: " << i << " Grade(s)." <<endl;
    }
    cout << "Minor Sum: " << minorG << endl;
    return 0;
}

This is what I have so far and the trouble I am having is within the for loop which is where my array is and where I am trying to get the sum of it. When I compile and run I get a sum of 138,427. Any help would be greatly appreciated!

Upvotes: 1

Views: 962

Answers (1)

Tas
Tas

Reputation: 7111

I think you're over-complicating things with dynamic arrays. I'll explain what you're doing, and try to provide help for what I think you're trying to do.

In your code int* minorGA = new int[minorG]; you are allocating memory for minorG amount of ints. There are two problems here:

  1. You are accessing an element outside of the memory you allocated. When you allocate 10 elements, you can access elements 0-9. Trying to access 10 is undefined behaviour (you are trying to access parts of memory that could contain anything).
  2. The values stored in this array are just whatever is in memory, so when you are attempting to increment minorG by the amount of one of these, it's just whatever is in memory at the time.

A separate problem is that you are not deallocating the memory, but some might argue that it isn't really a problem.

You should just be able to have the following to perform what I think you're trying to do:

for (int i = 0; i < 10; ++i)
{
    int inputtedNumber = 0;
    cout << "Enter a number" << endl;
    cin >> inputtedNumber;

    // add that number to some tally:
    finalTally += inputtedNumber;
}

Or if you are trying to store the elements in an array, you can use the following:

const int maxElements = 10;
int grades[maxElements] = {}; // this will construct all elements with 0. Without this, the elements may contain any number.
for (int i = 0; i < maxElements; ++i)
{
    int inputtedNumber = 0;
    cout << "Enter a number" << endl;
    cin >> inputtedNumber;

    // Store the number
    grades[i] = inputtedNumber;
}

In saying that, it will be better to use std::vector (knows its size, handles memory for you, can grow):

std::vector<int> grades;
// Allow the user to enter as many numbers as they'd like
for (;;)
{
    int input = 0;
    cout << "Enter a number" endl;
    cin >> input;
    // Store the number. Will continue to grow
    grades.push_back(input);
}

Upvotes: 1

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