Unable to see result of program, pause not working. Please advise

Question

I am trying to create a program that computes a students grades and gives you the result. I am doing this as part of a task from a book called "Accelerated C++".

The problem I am encountering at the moment is that I enter mid term and final exam scores as well as homework scores and it seems to calculate the final grade. However it closes before I can read it. I tried adding a pause using cin.get(); at the end but it didn't work.

#include <iomanip>
#include <ios>
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>


using std::cin;             
using std::cout;
using std::endl;
using std::setprecision;
using std::string;
using std::streamsize;
using std::vector;
using std::sort; 


int main()
{
//ask for and read the students name
cout << "Please enter your first name: ";
string name;
cin >> name;
cout << "Hello, " << name << "!" << endl;

//ask for and read the midterm and final grades 

cout << "Please enter your midterm and final exam grades: ";
double midterm, final;
cin >> midterm >> final;

//Ask for their homework grades 

cout << "Enter all your homework grades, "
    "followed by end-of-file: ";

vector<double> homework;
double x;
// Invariant: Homework contains all the homework grades read so far
while (cin >> x)
    homework.push_back(x);

// Check that the student entered some homework grades
typedef vector<double>::size_type vec_sz;
vec_sz size = homework.size();
if (size == 0) {
    cout << endl << "You must enter your grades. "
        "Please try again." << endl;
    return 1;
}

// Sort the grades 
sort(homework.begin(), homework.end());

// Compute the median homework grade
vec_sz mid = size / 2;
double median;
median = size % 2 == 0 ? (homework[mid] + homework[mid - 1]) / 2
    : homework[mid];


// compute and write the final grade
streamsize prec = cout.precision();
cout << "Your final grade is " << setprecision(3)
    << 0.2 * midterm + 0.4 * final + 0.4 * median
    << setprecision(prec) << endl;

cin.get();

return 0;

}

Is there a way to add a pause at the end so that I can see the result? Any help would be greatly appreciated. The code it exactly the same as the book. I just don't understand why it isn't working. Can anyone help?

Regards

Answer 1

You have to clear the stream state before using the stream again. The input operation that happened prior to cin.get() (i.e while (cin >> x)) continued to run until the stream state was no longer in a non-fail state. You need to clear() the stream state for it to be used again for I/O:

std::cin.clear();
std::cin.get();

Answer 2

You are asking your user for an end of file to end the input. Once this end of file is provided, your cin stream does no longer accept input. May be you find another way to end your data entry loop !

cout << "Enter all your homework grades, "
    "followed by -1 : ";

...
while ((cin >> x) && x>=0)
...
         // the enter after your last number would let get() return, so:  
cin.ignore(std::numeric_limits<streamsize>::max(), '\n');  // clear input until '\n' 
cin.get();

Variant, with a string based input loop:

As you know alread strings, you can opt for a line by line entry. So you'd read a string per line. This allows you to check if there's an empty line and exit the loop. The drawback of this approach is that you must convert your string to a numer.

cin.ignore(std::numeric_limits<streamsize>::max(), '\n');  // clear previous '\n' 
cout << "Enter all your homework grades, "
    "followed by an empty line : ";
...
string str; 
while (getline(cin, str) && str!="") 
    homework.push_back(stod(str));  // convert string to double
...  // and end of programme as above