Error Messages

[Steve3232]

Hey guys, I've got this code I'm working on for homework and it's pretty complete I just can't seem to figure out how to fix these error messages.

Here's the code.

#include <iostream>
#include <stdlib.h>
using namespace std;


int main ()

{
    int n=0,n_initial; // n will be the number of assignments entered in the system.
                     // since n will be counting down, I want to save n_initial as well.
    
// # OF EXERCISES
cout << "How many exercises to input?  >  ";
cin >> n;
n_initial = n;

int grades [2][n]; // 2 rows for possible and actual, n columns because you will have a column for each item.



//SCORE RECIEVED COUNTDOWN
while (n>0)

{
      int x,y;
cout << endl << endl << "Score recieved for exercise " << n << ":   ";
cin >> x;
grades [0][n] = x;
cout << endl << "Points possible for exercise " << n << ":  ";
cin >> y;
grades [1][n] = y;

n = n-1;
}

//CALCULATION OF TOTAL AND PERCENT
double score_total=0,pointspossible_total=0,rows_1,rows_2;

//SCORE TOTAL
int xy=0;
n = n_initial;

for (int xy=0; xy < n_initial; xy++)
{
    score_total += grades [0][n];
    n--;
}
    cout << endl << "Score Total = "<< score_total << endl;

//POINTS POSSIBLE TOTAL
xy=0;
n = n_initial;

for (int xy=0; xy < n_initial; xy++)
{
    pointspossible_total += grades [1][n];
    n--;
}
    cout << "Possible points Total = " << pointspossible_total << endl;
    cout << "Your total is " << score_total << " out of " << pointspossible_total << ", and your percentage is " << (score_total/pointspossible_total)*100 << "%" <<endl;
    system ("pause");
return (0);
}

And I'm getting these errors.

(17): error C2057: expected constant expression
(17): error C2466: cannot allocate an array of constant size 0
(17): error C2133: 'grades' : unknown size

Any help at all on how to fix this would be much appreciated!

[cire]

Use a vector or dynamically allocated memory for the array. It is not legal C++ to declare an array whose size cannot be determined at compile time.

[Steve3232]

Yeah I've been reading this, but I'm not quite sure how to implement the array while still getting the desired results.

I know that its something like

vector<int> grades (0,n);

Would this work the same as an array?

[Steve3232]

It just doesn't seem to work because once I create the vector, every time I try to use the vector later in the code it doesn't seem to accept it.

[cire]

I would suggest doing something like the following:

#include <iostream>
#include <vector>
using namespace std;

struct score_info
{
    int earned ;
    int max ;
};

int main ()

{
    int n=0; 
    cout << "How many exercises to input?  >  ";
    cin >> n ;

    vector<score_info> grades ;

    //SCORE RECIEVED COUNTDOWN
    while (grades.size() < n)
    {
        score_info score ;
  
        cout << "\n\nScore recieved for exercise " << n << ":   ";
        cin >> score.earned ;
 
        cout << "\nPoints possible for exercise " << n << ":  ";
        cin >> score.max ;

        grades.push_back(score) ;
    }

    // ...

    // Now you may access the vector like so:
    // grades[index].earned or grades[index].max to get at the members of the struct.