Open a file program w/ while loop C++

Question

so here are my instructions to create a while loop to open a file called ‘G:/points.dat’

This is my code so far. I'm struggling to create the for loop that reads through the file, prints them to the monitor and then using those integers as x, y points. I can understand naming the x and y parameters, but im struggling with the loop itself

#include "Window.h"
#include "Colours.h"
#include <fstream>
#include <iomanip>
#include <string>

using namespace std;

int main(int argc, char * argv[]) {
// create a new window of size 500 x 500 pixels
// the top left corner of the window is (0,0)
    SPA::Window window(500,500,"My Test");
    ifstream myInputFile;
    string inputFileName = "G:/points,dat";

    myInputFile.open(inputFileName);

    int i = 0;
    myInputFile >> i;

    myInputFile.close();

    window.show(argc,argv);

    return Fl::run();
}

Open file ‘G:/points.dat’
Read in multiple pairs of numbers – ie two numbers per line until the end of the file
You should use a while loop and appropriate tests of the file state to detect the end of file
the eof flag only gets set to true after you have tried to read at least one value beyond the end of the file.
Each pair of numbers represents the x and y coordinates (x,y) of a point on a line to be drawn.
- Inside your loop add a point to the current line for each (x,y) value you read in

You need a type that represents points and a collection of such points. — molbdnilo, Feb 16 '18 at 18:53
After following molbdnilo's recommendation, [give Option 2 of this linked answer](https://stackoverflow.com/a/7868998/4581301) a read for ideas on how to load the point-containing type. Also worth [looking into creating a `>>` overload](https://stackoverflow.com/questions/4421706/what-are-the-basic-rules-and-idioms-for-operator-overloading) for this type because it can turn the main program logic into a dead-stupid `while` loop. — user4581301, Feb 16 '18 at 19:12

score 2 · Answer 1 · answered Feb 16 '18 at 19:11

The loop is easy enough

while (myInputFile >> x >> y)
{
    // do something with x and y
    ...
}

That loop doesn't strictly read two values per line, it just reads the next two values whether they are on the next line or not.

BTW you have a typo in your code

string inputFileName = "G:/points,dat";

should be

string inputFileName = "G:/points.dat";

When you open a file you should always check to see if it opened successfully.

Open a file program w/ while loop C++

1 Answers1