Program 16

[pacman169]

Hello,

I have written a code that is probably filled with errors but I haven`t had much time lately looking to C++ so that could be expected.

Here is the description:

Write a program that consists of a while-loop that (each time around the loop) reads in two ints and then prints them out. Exit the program when a terminating | is entered.

Here is my version:

  #include<iostream>

int main()

{

int a=0;
int b=0;
cout<<" Enter two integer values ";
cin>>a>>b;

while { (a<100 || b<100) }

cout<< "a" && "b" ;

cout<< "To quit the program, enter |";
cin>>|;
terminate(); 

}

[mutexe]

you aren't doing anything in your while loop.

asking the user, testing the input, outputting to the screen ALL has to be done inside your loop.

[Aceix]

The use of terminate() here is not advisable. Use return instead.
Also, the syntax of while loops is
while(/*condition*/){/*statement to execute if condition is met*/}

Aceix.

[MikeyBoy]

mutexe wrote:

you aren't doing anything in your while loop.

... except writing to nstandard output the result of evaluating "a" && "b". "a" and "b" are both string literals, so evaluate as non-zero pointers. "a" && "b" will therefore always evaluate to true.

This means that whenever a or b is less than 100, you'll get an infinite loop which repeatedly writes "1" to stdout.

[pacman169]

Yes I got lost. Here is my code improved, sorry for not better quality, getting many errors when trying to compile

#include<iostream>

int main()

{

int a=0;
int b=0;

while  (a<100 || b<100) {

cout<<" Enter two integer values ";
cin>>a>>b;
cout<< "a" && "b" ;}

cout<< "To quit the program, enter |";
return 0; 

}

[MikeyBoy]

Did you really mean this:

cout<< "a" && "b" ;

?

Did you actually read my description of what this line does?

[pacman169]

 #include<iostream>
using namespace std;

int main()

{

int a=0;
int b=0;

while  (a<100 || b<100) {

cout<<" Enter two integer values ";
cin>>a>>b;
cout<< "a" and "b" ;

cout<< "To quit the program, enter |";
cin.get();
return 0; 

}

}

now it compiles but does not follow the original description.

[MikeyBoy]

cout<< "a" and "b" ;

The C++ operator and is synonymous with the operator &&.

In other words, it's still doing exactly the same thing as the previous version, which I explained to you earlier in the thread.

[pacman169]

Well, I`m not sure what I should use then. Is it otherwisely correct? The terminating | was also a bit confusing.

[MikeyBoy]

You know how to stream more than one item from an istream. Hint: streaming more than one item into an ostream is very similar.

Your program will only ever perform one pass through the loop, since you have return 0; within your loop.

[pacman169]

I fixed the line 15 to cout<<a<<b.

2) I can`t associate entering | to return 0;

Maybe use an if-statement?

[MikeyBoy]

Yes, exactly.

Forget about the code for a moment, and just think about it logically. You want to read the user's input, and then make a decision based on what the user enters.

Making a conditional decision usually means using an if statement.

[xenovia12]

You're code saying that your while loop is a mess but not really. You did just put a while loop but did not have a statement ^^

[pacman169]

 #include<iostream>
using namespace std;

int main()

{

int a=0;
int b=0;

while  (a<100 || b<100) {

cout<<" Enter two integer values ";
cin>>a>>b;
cout<<a<<b ; }

cout<< "To quit the program, enter |";

if (cin>>|)  return 0;

else {}                                   // Do nothing


}

[MikeyBoy]

A couple of points:

1) The symbol | on its own is the bitwise OR operator. If you want to treat it as a character, you need to surround it in single quotes, the way you would any other character. If you want to treat it as a string containing a single character, you need to surround it with double-quotes, like any other string.

Does that line even compile?

2) Even if you treated it as a string, if (cin>>"|") wouldn't do what you seem to think it does. If you look at the reference for the >> operator for the istream class:

http://www.cplusplus.com/reference/istream/istream/operator%3E%3E/

you'll see that the return value is the istream object itself. ANd if you look at the reference for the overloaded bool operator for the class:

http://www.cplusplus.com/reference/ios/ios/operator_bool/

you'll see that it tests for whether an error flag on the stream has been set.

What you want to do is:

- use cin to read the user input into a variable
- test the value of the variable to see whether the user typed a | character.

I strongly recommend you go back to your textbook and try and get a better understanding of how to use I/O streams.

[pacman169]

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

int main()

{

int a=0;
int b=0;

while  (a<100 || b<100) {

cout<<" Enter two integer values ";
cin>>a>>b;
cout<<a<<b ; }

cout<< "To quit the program, enter |";

char '|'
cin>> '|'

ifstream |;

if (|) return 0;
    
else {}
   
  
}

[Aceix]

char '|'
cin>> '|'

ifstream |;

if (|) return 0;

else {}

This makes zero sense.

Aceix.

[MikeyBoy]

MikeyBoy wrote:

I strongly recommend you go back to your textbook and try and get a better understanding of how to use I/O streams.

OK, I'm going to have to revise that. I don't mean to sound harsh, but I think you need to go right back to the fundamentals of C/C++ programming, so that you understand what a variable is, how you define them, how you assign values to them, etc.

Lines like:

char '|'
cin>> '|'

ifstream |;

if (|) return 0;

are simply meaningless - they're not C or C++, and they have no meaning. It honestly looks like you're just typing anything you can think of, and hoping to magically stumble across a combination of characters that works. You will never, ever, be able to successfully program like that.

I know you've said that you haven't had much time lately to practice programming, but there's not really any way around it: you need to go back to the basics, and re-learn them.

[pacman169]

Should be something like this:

#include<iostream>

using namespace std;

int main()

{

int a=0;
int b=0;

while  (a<100 || b<100) {

cout<<" Enter two integer values ";
cin>>a>>b;
cout<<a<<b ; }

cout<< "To quit the program, enter |";

char |= 'a'
cin>> a                         // a is a variable


if ( a ==  '|')

return 0;

else {}


}

[MikeyBoy]

char |= 'a'
cin>> a                         // a is a variable 

I can only re-iterate my previous comments. If you can't even remember how to declare a simple character variable, you need to go back and re-learn the basics.