用于扫描数字数组的算法，并计算在范围（0 - 24）（25 - 49）​​等之间的数量

Question

New Member to the site, but an active searcher of the site to find answers.

This one is a bit confusing for me to figure out... Hopefully after reading the source file you can help with my dilemma.

Program: Store an array of numbers (manually/from file); Scan the array and count the numbers between certain ranges. (0-24, 24-49, 50-74 and so on until 200); Then display the count either on screen or saved to a .txt file.

    // Program for teachers to input test grades.
    // Test scores range from 0-200.
    // Test scores can either be input by file, or manually.
    // Program will then display the number of test scores that falls
    //  into quarter ranges.
    // Display options are either on screen or in file.


    #include "stdafx.h"
    #include <iostream>
    #include <fstream>

    using namespace std;

    // Due to being new with functions, I was not sure if these variables
    //  need to be constant or not...
    char scores;
    int students;
    int i,n, list[100];
    void openinfile(ifstream &infile);
    void openoutfile(ofstream &outfile);
    int count(int x, int y);
    ifstream inputfile;
    ofstream outputfile;

    // Using VS2013
    // Main program for options menu's and algorithms.
    int main(int argc, char *argv[])
    {


int total;
int qMenu1;
int qMenu2;




cout << "How many students are in your class?" << endl;
cin >> students;
cout << "How would you like to enter your test scores?" << endl;
cout << "1 - From File." << endl;
cout << "2 – Manually." << endl;
cin >> qMenu1;

if (qMenu1 = 1)
    openinfile(inputfile);

else if (qMenu1 = 2)
{   
    cout << "Please enter total number of students." << endl;
    cin >> students;            // Store array size in students.


    // Sets up the array for the user to enter all grades, 1 by 1
    // until the the entries = max number of array slots.
    for (i=0; i<students-1; i++)    
    {
        cout << "Enter test score #" << i << ":" << endl;
        cin >> list[i];
    }
}
else 
{
    cout << "Please enter a valid Number." << endl;
    cout << "(1 or 2)" << endl;
}



// Menu2: Display options. (On Screen or Save to File)
cout << "How would you like your results displayed?" << endl;
cout << "1 – On Screen." << endl;
cout << "2 – To File." << endl;
cin >> qMenu2;

if (qMenu2 = 1)
{
    cout << "TOTAL NUMBER OF STUDENTS WITHIN RANGE:" << endl;
    cout << endl;
    total = count(0, 24);           // Quarter ranges that the input 
    cout << "000 – 024\t" << total << endl; // needs to be checked against.
    total = count(25, 49);
    cout << "025 – 049\t" << total << endl;
    total = count(50, 74);
    cout << "050 – 074\t" << total << endl;
    total = count(75, 99);
    cout << "075 – 099\t" << total << endl;
    total = count(100, 124);
        cout << "100 – 124\t" << total << endl;
    total = count(125, 149);
        cout << "125 – 149\t" << total << endl;
    total = count(150, 174);
        cout << "150 – 174\t" << total << endl;
    total = count(174, 200);
        cout << "174 – 200\t" << total << endl;
}   
else
{
    openoutfile(outputfile);    

    outputfile << "TOTAL NUMBER OF STUDENTS WITHIN RANGE:" << endl;
    outputfile << endl;
    total = count(0, 24);
    outputfile << "000 – 024\t" << total << endl;
    total = count(25, 49);
    outputfile << "025 – 049\t" << total << endl;
    total = count(50, 74);
    outputfile << "050 – 074\t" << total << endl;
    total = count(75, 99);
    outputfile << "075 – 099\t" << total << endl;
    total = count(100, 124);
        outputfile << "100 – 124\t" << total << endl;
    total = count(125, 149);
        outputfile << "125 – 149\t" << total << endl;
    total = count(150, 174);
        outputfile << "150 – 174\t" << total << endl;
    total = count(174, 200);
        outputfile << "174 – 200\t" << total << endl;

    outputfile.close();     

    return 0;
}

    }

// Function to open file for reading and input in array.
void openinfile(ifstream &infile)
{
    char filename[100];

    cout << "Enter the file name: ";
    cin >> filename;
    infile.open(filename);

    if (infile.fail())
        cout << filename << "\tDoes not exist" << endl;

    else
    {
        cout << filename << "Successfully open" << endl;
    // read character until the end of file.
        for (int i = 0; i < 100; i++) 
        {
            infile >> list[i];
        }
    }
}

// function to open new file for writing result to.
void openoutfile(ofstream &outfile)
{
    char filename[100];

    cout << "Enter the file name to save.";
        cin >> filename;

    outfile.open(filename);
    if (outfile.fail())
    {
        cout << filename << " could not be saved." << endl;
    }
    else
    {
        cout << filename << "Successfully saved!" << endl;
    }
}

// function to count numbers within a certain range.
int count(int x, int y)         // ((x >= 0)&&(x <= 24))
{
    int numOf = 0;              // variable counter
    int target;



    target = (( target >= x)&&(target <= y));

    for(int cntr = 0; cntr < students; cntr++)  
    {
        if(list[students] == target)
        {
            numOf += 1; // adds 1 for every number found between
        }                       // range target.
        return numOf;           // returns number of occurances found.
    }
}

The last function is where my problem lies, I'm not quite sure how to go about this. Any help would be wonderful! -Chris-

Answer 1

You got confused about the comparison:

target = (( target >= x)&&(target <= y));

target is undefined, but you are checking if it is in the desired range and then setting it to a boolean value. You are then testing whether any element of the array is equal to that value. Also, you're returning inside the loop after the first iteration.

Let's fix all this, and I'm sure you'll realise that it's just late at night and you've had too much coffee and you weren't thinking straight:

int count(int x, int y)
{
    int numOf = 0;
    for(int cntr = 0; cntr < students; cntr++) {
        if( list[ctr] >=x && list[ctr] <= y ) numOf++;
    }
    return numOf;
}

Now, there are way better ways to do this. For example, you could count ALL the ranges in one loop by using integer division. If you know for sure that all your values are in the valid range, it can be as simple as this:

int counts[8] = {0};
for( int i = 0; i < students; i++ ) counts[list[i]/25]++;

Also, there's no reason to duplicate your code that outputs just because you're writing to a stream. Move the code into a function:

void output( ostream & s ) {
    s << "TOTAL NUMBER OF STUDENTS WITHIN RANGE:" << endl;
    // etc...
}

Then:

if (qMenu2 = 1)
{
    output(cout);
} else {
    openoutfile(outputfile);
    output(outputfile);
    outputfile.close();
}

Answer 2

Rather than fix the code itself, what you're looking at is called a Bucket Sort . You want an set of counters, rather than just one, and you want to use your input numbers to determine which counter to increment.

You have a huge advantage, here, if I'm reading your introduction correctly. Your "buckets" are for a continuous range of numbers, each range being of equal size.

So, if you haven't already figured it out from that, you would want an array of counters and you can use integer division by 25 to find the index of each bucket.

That should also be more straightforward than keeping the comparisons straight.