Thread: use of WHILE loop to read the grades

Hi

I was trying to learn the use of WHILE loop. Given below is the simple program I tried to write. The first problem is even when I enter the Roll No. to be "10000" the program doesn't terminate. Secondly, what suggestion(s) or advice(s) do you have for me to improve the program, or learning these WHILE, FOR, DO loops? Please let me know. Thanks a lot.

Code:

// use of WHILE loop to read the grades

#include <iostream>
#include <cstdlib>

using namespace std;

int main()
{
      
	  int RN;
	  float M;
      
	  while(RN != 10000)
      
	  { 		   
      cout << "Enter the roll no.: ";
      cin >> RN;
      
	  cout << "Enter the marks: ";
      cin >> M;
      
      if ( M > 80 )
      cout << "A Grade" << endl;
      
	  else if ( M > 70 )
      cout << "B Grade" << endl;
      
	  else if ( M > 60 )
      cout << "C Grade" << endl;
      
	  else if ( M < 60 )
      cout << "F Grade" << endl;
      }

      system("pause");
   
}

Thanks, manasij.

But it doesn't terminate even when the entered Roll No. is 10000. Why is so? Please tell me.

Hi Jim

You are right the program only runs once when I enter the RN = 10000.

Should I insert an if statement after:

Code:

cout << "Enter the roll no.: ";
cin >> RN;

to stop the program from proceeding any further? But how do I get out of the loop (if RN == 100)? I think I have read somewhere that there is some "break" word to do it. Don't know how to use it or it is the right keyword to do get out of the loop. Please guide me here.

And secondly I don't get that initialization part of the variables. Yes, I didn't initialize them but you said (or as far as I can understood it) that I already initialized the RN by saying (while RN != 10000). But this is only a condition statement, what does it have to do with the initialization? Please guide me with it too.

Thanks a lot.

Originally Posted by jimblumberg

But he is using the initial value.

Code:

while(RN != 10000)

RN has not been initialized it could be anything, 10000 even.
Jim

Thanks, Jim.

Please have a look on the below code. And please let me know if you find something wrong (it works okay on my end), or if you have some advice. I'm new to these loops world so I think so suggestions and advices are important.

I couldn't understood the purpose of the bold part in the quotes post. I understand you were trying to warn about something but couldn't get it. Please shed some light on it.

And by the way, is using "return 0;" with int main() compulsory or optional? What is your opinion? It could be a good things to do but is it really compulsory? Please tell me.

Thank you so much for helping me in so many problems.

Best wishes
Jackson

Code:

// use of WHILE loop to read the grades

#include <iostream>
#include <cstdlib>

using namespace std;

int main()
{
      
	  int RN;
	  float M;
      
	  while(RN != 10000)
      
	  { 		   
      cout << "Enter the roll no.: ";
      cin >> RN;
      
	  cout << "Enter the marks: ";
      cin >> M;
      
      {
   	  if ( RN >= 10000 )
        break;
      }
      
      if ( M > 80 )
      cout << "A Grade" << endl;
      
	  else if ( M > 70 )
      cout << "B Grade" << endl;
      
	  else if ( M > 60 )
      cout << "C Grade" << endl;
      
	  else if ( M < 60 )
      cout << "F Grade" << endl;
      }
      
      cout << "Job Done" << endl;

      system("pause");
   
}

Originally Posted by jackson6612

Please have a look on the below code. And please let me know if you find something wrong (it works okay on my end), or if you have some advice.

The problem that jimblumberg mentioned is still there: you compare RN to 10000 before RN has been given an initial value. This works most of the time, but will fail in the special case that the garbage value that RN has at that point is 10000. One solution to this is to initialise RN to say, 0. Another solution is to use a do while loop.

Originally Posted by jackson6612

And by the way, is using "return 0;" with int main() compulsory or optional?

Optional.

Oh, and you need to indent your code better, e.g.,

Code:

// use of WHILE loop to read the grades

#include <iostream>
#include <cstdlib>

using namespace std;

int main()
{
    int RN;
    float M;

    while(RN != 10000)
    {
        cout << "Enter the roll no.: ";
        cin >> RN;

        cout << "Enter the marks: ";
        cin >> M;

        {
            if ( RN >= 10000 )
                break;
        }

        if ( M > 80 )
            cout << "A Grade" << endl;

        else if ( M > 70 )
            cout << "B Grade" << endl;

        else if ( M > 60 )
            cout << "C Grade" << endl;

        else if ( M < 60 )
            cout << "F Grade" << endl;
    }

    cout << "Job Done" << endl;

    system("pause");
}

Originally Posted by manasij7479

int RN(0)
and what are the "{ }" around the if block for ?

What is that bold thing? I understand it's a function call with argument "0".

I shouldn't have used the braces with the single statement after the if. But using "{ }" with multi-statements after the if is must. Isn't it?

Originally Posted by laserlight

The problem that jimblumberg mentioned is still there: you compare RN to 10000 before RN has been given an initial value. This works most of the time, but will fail in the special case that the garbage value that RN has at that point is 10000. One solution to this is to initialise RN to say, 0. Another solution is to use a do while loop.

That "garbage" part made everything clear. I didn't know that the computer also has garbage in the empty places! Thanks a lot for telling me this.

So far I haven't learned the use of the do while loop. But I'm sure will learn tomorrow!

Originally Posted by laserlight

Oh, and you need to indent your code better

I understand the problem. But as I mentioned in some other post that when I paste the code here something goes wrong. I don't know why.

Originally Posted by jimblumberg

You should always initialize your variables when you define them.

I will follow your advice from now on. Thanks for advising me.

Originally Posted by jimblumberg

I don't think you understand the brace placement. In this snippet you are creating a block around the if statement which is not required. You probably want the braces to belong to the if statement.

I get your point but don't you think it's a good practice (just for the sake of consistency) to use braces around the block of the if statement even when the block consists of only one statement? Please advise me.

Thank you everyone for all the help.

Best wishes
Jackson