Question

I just finished my first assignment using arrays and I feel like it is a little more complex than it has to be. The program reads a file with scores in it and counts the occurrences of a score within a certain range and then outputs the number of occurrences.

I am wondering if there is a more efficient way of completing this task (using only arrays).
I understand the array saved me from having to make 8 separate variables but there are still so many if statements!!

header

#ifndef HEADER_H_INCLUDED
#define HEADER_H_INCLUDED

#include <iostream>
#include <iomanip>
#include <fstream>
#include <cctype>
#include <cstdlib>

using namespace std;

void extern input(ifstream&, ofstream&, int&, int*);
void extern calculate (int, int*);
void extern output (ofstream&, int*);


#endif // HEADER_H_INCLUDED

main

#include "header.h"

int main()
{
    int grade;
    int array[8] = {0};
    ifstream inData;
    ofstream outData;

    inData.open("Ch9_Ex4Data.txt");

    if (!inData)
    {
        cout << "Cannot open the input file."
             << endl;
            return 1;
    }

    outData.open("DataOut.txt");

    while (inData)
    {
        input(inData, outData, grade, array);
    }

    output (outData, array);

    system("PAUSE");
    return EXIT_SUCCESS;

}

input

#include "header.h"

void input(ifstream& inData, ofstream& outData, int& grade, int array[])
{
    while(inData >> grade)  // while a grade is read
    {
     calculate(grade, array);
    }
}

calculate

#include "header.h"

void calculate (int grade, int array[])
{
    int index;

        if (grade >= 0 && grade < 25)
        {
        index = 0;
        array[index]++;
        }
        else if (grade >= 25 && grade < 50)
        {
        index = 1;
        array[index]++;
        }
        else if (grade >= 50 && grade < 75)
        {
        index = 2;
        array[index]++;
        }
        else if (grade >= 75 && grade < 100)
        {
        index = 3;
        array[index]++;
        }
        else if (grade >= 100 && grade < 125)
        {
        index = 4;
        array[index]++;
        }
        else if (grade >= 125 && grade < 150)
        {
        index = 5;
        array[index]++;
        }
        else if (grade >= 150 && grade < 175)
        {
        index = 6;
        array[index]++;
        }
        else if (grade >= 175 && grade <= 200)
        {
        index = 7;
        array[index]++;
        }
}

output

#include "header.h"

void output (ofstream& outData, int array [])
{
    outData << "number of students with score of 0-24 is " << array[0] << endl;
    outData << "number of students with score of 25-49 is " << array[1] << endl;
    outData << "number of students with score of 50-74 is " << array[2] << endl;
    outData << "number of students with score of 75-99 is " << array[3] << endl;
    outData << "number of students with score of 100-124 is " << array[4] << endl;
    outData << "number of students with score of 125-149 is " << array[5] << endl;
    outData << "number of students with score of 150-174 is " << array[6] << endl;
    outData << "number of students with score of 175-200 is " << array[7] << endl;
}

Answer 1

You’re right, because they’re evenly spaced it could be a LOT shorter, e.g.

void calculate (int grade, int array[])
{
    if (grade >= 0 && grade < 200) {
        index = grade / 25;
        array[index]++;
    }
    else if (grade == 200)
        array[7]++;
}

output() could be turned into a loop, the calculation for high and low of each bin is straightforward (using multiplication).

If the bins weren’t equally spaced, you’d need to use a lookup table like Serge’s suggestion.