Question

I am learning about pointers and arrays in class. My trouble is in the dupScore function.
I am trying to find the number of students who have the same score. scoreArrays element number identifys the student and holds the score.

I want to create a new array to use the students score as the index to the array. I get a red squiggly under scoreArrays though. The error is “expression must be integral or enum”

for(int count = 0; count < maxStudents; count++)
        comparisonArray[scoreArray[count]]++;

Here is my whole code.

#include <iostream>
using namespace std;

const int maxStudents = 30;
void readScores(double[]);
void gradeCounter(double[],int&,int&,int&,int&,int&);
int dupScore(double[]);
void readoutFunc(double[], int, int, int, int, int, int);

int main()
{
    int As = 0, Bs = 0, Cs = 0, Ds = 0, Fs = 0; // Distribution of scores
    int sameScore = 0;

    double scoreArray[maxStudents];
    readScores(scoreArray);//Read in Scores
    gradeCounter(scoreArray, As, Bs, Cs, Ds, Fs);//Count letter grades
    sameScore = dupScore(scoreArray);//Detect duplicate scores

    system ("PAUSE");
    return 0;
}


void readScores(double scoreArray[])
{
    double *scorePTR;
    scorePTR = scoreArray;

    for(int count = 0; count < maxStudents; count++)
    {
        cout<<"Please enter score for student "<<count+1<<" or -999 to end.\n";
        cin>>*(scorePTR+count);
        if(*(scorePTR+count) == -999)
        break;
    }
 }



void gradeCounter(double scoreArray[],int &As,int &Bs,int &Cs,int &Ds,int &Fs)
{
    double *scorePTR2;
    scorePTR2 = scoreArray;

    for(int count = 0; count < maxStudents; count++)
    {
        if(scoreArray[count] >= 90)
            As+=1;
        else if(*(scorePTR2+count) >= 80 && *(scorePTR2+count) < 90)
            Bs+=1;      
        else if(*(scorePTR2+count) >= 70 && *(scorePTR2+count) < 80)
            Cs+=1;
        else if(*(scorePTR2+count) >= 60 && *(scorePTR2+count) < 70)
            Ds+=1;
        else if(*(scorePTR2+count) >= 0 && *(scorePTR2+count) < 60)
            Fs+=1;
    }
}

int dupScore(double scoreArray[])
{
    const int maxGrade = 101;
    double comparisonArray[maxGrade];
    int sameScores = 0;


    for(int count = 0; count < maxStudents; count++)
        comparisonArray[scoreArray[count]]++;

    for(int count2 = 0; count2 < maxGrade; count2++)
    {
        if(comparisonArray[count2] > 0)
            sameScores+=1;
    }


        return sameScores;

}

void readoutFunc(double scoreArray[], int As, int Bs, int Cs, int Ds, int Fs, int sameScore)
{
        int numofStudents = 0;
    for(int count = 0; scoreArray[count] >= 0; count++)
    { 
        numofStudents += 1;
    }
    cout<<"\n\nReport";
    cout<<"\n---------";
    cout<<"\nNumber of students: "<<numofStudents;
    cout<<"\nNumber of As: "<<As;
    cout<<"\nNumber of Bs: "<<Bs;
    cout<<"\nNumber of Cs: "<<Cs;
    cout<<"\nNumber of Ds: "<<Ds;
    cout<<"\nNumber of Fs: "<<Fs;

    cout<<"\n\n"<<sameScore<<" students have the same score."
}

Answer 1

scoreArray is defined as double[] so scoreArray[count] will give you a double. You’ll need an integer to be able to reference an element from the comparisonArray.

for(int count = 0; count < maxStudents; count++)
comparisonArray[(int)scoreArray[count]]++;

That will fix the problem you are currently facing, but it will also lose a lot of precision. You might look at changing the double[] to an int[] if grades are always integers. Otherwise you might need to look at a different method of matching elements of the scoreArray.