From: "Chris McKenzie" <taganov AT earthlink DOT net>
Newsgroups: comp.os.msdos.djgpp
Subject: Newbie DJGPP compiler question
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Date: Thu, 15 Jun 2000 13:34:17 GMT
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To: djgpp AT delorie DOT com
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Reply-To: djgpp AT delorie DOT com

    The question I have requires a little explanation first.  I am taking
C++ in college right now--and I was given some excercise program to write,
but it was hard to tell if my output was correct because the screen would
simply flash the output and then put me back to the code screen.  I came up
with the idea of putting an extra "cin" command right before my return 0;
in "int main()" so that just prior to finishing, the program stops and lets
me look at the output.  This works just fine.
    Then I was reading in my textbook about how you can include "conio.h" to
look for a keyboard hit.  So I wrote a for-loop to replace my cin statement.
The for-loop looks for a keyboard hit prior to returning 0, and just waits.
I can hit any key--the for loop condition is met, and I return 0 and exit
the program. Here is an example:

#include <iostream>
#include <conio.h>           file://include so that program will maintain
                             file://user window until I press a key on
                             file://the keyboard
using namespace std;
int dummy;

int main()
{       int test, num, accum;
        test = 0;
        accum = 0;

        cout << "Please enter a number, and I will give you its
             sum of squares   \t";
        cin >> num;

        while(test < num){
             test++;
             accum = accum + (test * test);}

        cout << "The sum of squares for " << num << " is " << accum << ".
\n";

        for(dummy = 1; !kbhit(); dummy++);
        return 0;}

This program compiles and executes perfectly.  However, the following
program illustrates my problem perfectly:
#include <iostream>
#include <conio.h>
using namespace std;

int main()
{
        int integer1, integer2, result;
        char operation;

 //simple calculation program

        cout << "Please enter a number.   \n";
        cin >> integer1;
        cout << "\n Please enter an operator (+, -, *, /). \n";
        cin >> operation;
        cout << "\n Please enter a second number \n";
        cin >> integer2;

 //checks to make sure a correct operator is given before doing calculations

        if (operation)
           {if (operation == '+')
           {result = (integer1 + integer2);
           cout << integer1 << " " << operation << " "
                << integer2 << " = " << " " << result;}

           else if(operation == '-')
           {result = (integer1 - integer2);
           cout << integer1 << " " << operation << " "
                << integer2 << " = " << " " << result;}

           else if(operation == '*')
           {result = (integer1 * integer2);
           cout << integer1 << " " << operation << " "
                << integer2 << " = " << " " << result;}

           else if(operation == '/')
           {result = (integer1 / integer2);
           cout << integer1 << " " << operation << " "
                << integer2 << " = " << " " << result;}

           else
           {cout << "Invalid Operator!  No Operations Performed!";}
           }
        else
           {cout << "Invalied Operator!  No Operations Performed!";}

        int i;
        for(i=0; !kbhit(); i++);
        //cin >> operation;
        return 0;
        }       // close main function

In the second program--the order of program execution seems to be messed up.
It goes through the If-then sequence just fine--but it doesn't cout the
output until AFTER the kbhit condition is met.  Given that the cout
statement is INSIDE the curly braces INSIDE the else-if conditions, this
doesn't make any sense to me.  I know that Microsoft's Visual C++ has some
kind of prioritization between gets() and puts(), cin and cout such that one
command always gets executed first regardless of the actual sequence that
they occur in the code.  I wonder if perhaps DJGPP has some similar kind of
compilation algorithm that causes it to execute my for loop before
completing the if then structure.  Any ideas?

Thanks in advance;

Chris McKenzie