C++ Program Boolean? Error

Question

I'm supposed to write a program that reads student IDs and grades from a file, with 3 functions:

getResults: this function reads from the file and counts how many failed (if score < 55) calculates the average and returns the number of students.
display: displays everything to the screen
isF: checks whether the score is less than 55 and returns true if it is. (In other words, if the student failed it will return true.)

My program is working fine up to the checking how many failed. I'm almost certain its a logical error but I can't figure out where. The number of failed students is not being calculated correctly. I keep getting 1 when it is supposed to be 2 as per the sample file.

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

int getResults(ifstream &input, int &failed, double &average);
bool isF(int score);
void display(int num_students, double average, int num_failed);

int main() {
    int numfailed, numOfStudents;
    double avg;
    ifstream in_stream("grades.txt");

    numOfStudents = getResults(in_stream, numfailed, avg);
    display(numOfStudents, avg, numfailed);
    system("PAUSE");
    return 0;
}

int getResults(ifstream &input, int &failed, double &average) {
    int studentID, studentGrade, total = 0, numberOfStudents = 0;

    while (input >> studentID >> studentGrade) {
        total = total + studentGrade;
        numberOfStudents = numberOfStudents + 1;
        failed = isF(studentGrade);
    }
    average = total / numberOfStudents;
    return numberOfStudents;
}

bool isF(int score) {
    if (score < 55)
        return true;
    else
        return false;
}

void display(int num_students, double average, int num_failed) {
    cout << "Number of Students: " << num_students << endl;
    cout << "Class Average: " << average << endl;
    cout << "Number of students failed: " << num_failed << endl;
}

My sample file is as follows:

Sample output:

Number of students: 6

Class Average: 65

Number of students failed: 2

The output I'm getting is exactly the same except that I get 1 student failed.

My question is as follows, my program is working fine up to the checking how many failed. I'm almost certain its a logical error but I can't figure out where. What is your question? — Daqs
– Daqs, Commented Jun 6, 2015 at 7:21
You can replace if (score < 55) return true; else return false; with return (score < 55);. But you aren't counting failures. — David Heffernan
– David Heffernan, Commented Jun 6, 2015 at 7:30

Chnossos · Accepted Answer · 2015-06-06 07:34:47Z

3

First initialise your numfailed to 0 (thanks @ Peter), then change this:

failed = isF(studentGrade);

To this:

failed += isF(studentGrade);

Or this:

 failed += isF(studentGrade) ? 1 : 0;

edited Jun 6, 2015 at 7:34

answered Jun 6, 2015 at 7:24

Chnossos

10.7k4 gold badges32 silver badges41 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Peter Over a year ago

numFailed needs to be initialised to zero in main(). It is uninitialised - and not initialised to zero unless you explicitly do that..

Michael Burr Over a year ago

Get in the habit of initializing your variable in general (at least for C/C++).

mahmoudalsof Over a year ago

That fixed it! Thanks Chnossos and Peter!

Nivetha · Accepted Answer · 2015-06-06 07:29:27Z

1

There are two things you need to change. First initialize failed in your function to zero and then modify to add the count of failures. Here is the modified function:

int getResults(ifstream &input, int &failed, double &average)
{
    int studentID, studentGrade, total = 0, numberOfStudents = 0;
    failed = 0;

    while (input >> studentID >> studentGrade)
    {
        total = total + studentGrade;
        numberOfStudents = numberOfStudents + 1;
        failed += isF(studentGrade); //this ensures that every time a student fails, it is added
    }
    average = total / numberOfStudents;
    return numberOfStudents;

}

answered Jun 6, 2015 at 7:29

Nivetha

7085 silver badges17 bronze badges

Collectives™ on Stack Overflow

C++ Program Boolean? Error

2 Answers 2

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related