C++ loop help

Question

plang007 -5 Junior Poster in Training

15 Years Ago

After your program works correctly for one student, add a loop so the user can process any number of students. Prompt the user for the number of students to process; use that value to control the loop.

*How do I prompt the user for the number of students to process and use that value to control the loop.

#include<iostream>
 #include <string>
 #include <cmath>
 
 using namespace std ;
 
 string getName ();
 int averageScores( int);
 void printMessage (string, int);
 void tallyScores ( int,int&,int&,int&);
 
  int main()
   {
         const int NUMBER = 4;        // number of scores for each student 
         char moreStudents = 'y';
         string who;                 //name of the student
         int testAverage;
         int students;
         
         cout << "For each student, you will be prompted for a name and "<< NUMBER << " test scores\n" << endl; 
  
         while ( moreStudents =='y' || moreStudents == 'Y'){  
            
            who = getName () ;
            testAverage = averageScores ( NUMBER);
            printMessage ( who, testAverage );       
            cout << "\n\nMore students? Y or N: " ;
            cin >> moreStudents ;
            cout << endl;
            cin.ignore (10, '\n');
            }

      system ("pause");
      return 0;
   }     // end main
   /////////////////////////////////////////////////////////////////////
   // Prompts the user to input the student's name
   string getName ()
   {      
      string name ;
          
      cout << "Enter student name " ;
      getline ( cin, name);
      return name ;
   }       
   /////////////////////////////////////////////////////////////////////////////////////////////////////////////
   // this function inputs and averages scores. Parameter sum adds the scores up.
   
   int  averageScores( int sum )
   {     
      int score1, score2, score3, score4 ;
      int low;
      int rounded;    
      float average; 
      
      cout << "\nEnter four interger scores with a space in between: " ;
      cin >> score1 >> score2 >> score3 >> score4 ;
               
      cout << "\nThe test scores enetered are: " << score1 << " " << score2 << " " <<         score3 << " " << score4 << endl;
               
      sum = score1 + score2 + score3 + score4;
               
      low = score1;
    
      if(low > score2){
	     low = score2;
	     }
		  
      if(low > score3){
		 low = score3;
			
       	 }
	  if(low > score4){
		 low = score4;
			
	     }
	
      cout << "\nThe lowest score of " << low << " is dropped." << endl;
      
      average = (sum - low) / 3.0;
      cout << "\nThe average is " << average << " with three scores and the lowest score dropped." << endl;
      rounded =  static_cast<int>(average + 0.5);
      cout << "\nThis average is then rounded to " << rounded << "." << endl;
      return rounded;
  } // averageScores  /
  
  //////////////////////////////////////////////////////////////////////
  // adds to the appropriate count depeding on the score  
  void tallyScores ( int average, int& repeatIt,int& wow, int& passing)
  {
              				
    if(average <60)
       repeatIt++;
				
    else if(average >= 95)
       wow++;
       
    else if(60 <= average < 95)
       passing++;
    
}
/////////////////////////////////////////////////////
// Prints out a message for the student depending on the score
  void printMessage (string name, int average) 
  {
    string message ;
   	if(average <60)
        message = ("Gotta repeat it");
     
    else if(average >= 95)
		message = ("WOW");

    else if(60 <= average < 95)
        message = ("passing");
    				
    cout <<  "\nAverage for "  <<  name  << " is " << average << "; " << message; 
       
  }          //printMessage

c++

3 Contributors
9 Replies
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6 Hours Discussion Span
Latest Post 15 Years Ago Latest Post by NathanOliver

Dani AI

Generated 10 Months Ago

Root cause (quick): mixing formatted extraction (cin >>) with getline leaves the newline in the input buffer, so your first getline returns an empty string. In your Post #9 you also replaced the input of students with cin.get() (so students is never set) — that explains the blank name and the odd behavior. was right that you must consume the leftover newline; was right about the range-check bug.

Minimal, robust fixes to apply now

Read the number of students with the extraction operator, then immediately discard the rest of that input line before you call getline. A safe discard is cin.ignore(numeric_limits<streamsize>::max(), '\n'); (include <limits>).
Instead of relying on small fixed counts like ignore(10, '\n'), prefer the numeric_limits approach above or use the stream whitespace skipper before getline (for example getline(cin >> ws, name)) so a stray newline will be skipped reliably.

Other improvements to avoid future headaches

Do not use cin.get() in place of reading the student count — cin.get() just consumes one character and will not set students. Always do cin >> students; then clear the rest of the line.
Move the discard so it happens right after reading the count, and if you read the four integers inside averageScores, either discard the trailing newline there (again with ignore or ws) or use ws before the next getline.
Clean up the API: averageScores currently takes an int you immediately overwrite; either remove that parameter or use it consistently so the function signature matches its behavior.
Fix range tests: C++ does not support chained numeric comparisons. Use a logical AND for ranges (e.g., check that average is >= 60 AND < 95); otherwise the expression will be evaluated as a bool converted to an int and give surprising results.

Those four changes (read count, consume line, use ws/robust ignore, and fix the comparisons) will make the loop and name input behave predictably.

All 9 Replies

NathanOliver 429 Veteran Poster

15 Years Ago

instead of using a while loop ask the user for the number of students and then use that as the stop condition in a for loop

// in main
cout << "How many students do you want to enter: ":
cin >> numberOfStudents;
for (int i = 0; i < numberOfStudents; i++)
{
    // code for getting students goes here
}
// more code

Saith 74 Junior Poster

15 Years Ago

NathanOliver has a good point, just a for-loop.

Just in case you haven't done for-loops just yet, you can do basically the same thing with a while loop. Ask for the number of students, create an index for the current loop count, then increment the index once the loop ends. If the index is less than or equal to the amount of students, do the loop again; else the loop ends.

NathanOliver 429 Veteran Poster

15 Years Ago

After line 21 write cin.get() . The problem comes from having mixed input. For more information check this out.

Edited 15 Years Ago by NathanOliver because: n/a

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plang007 -5 Junior Poster in Training · Answer 1 · 2011-02-24T09:09:08+00:00

#include<iostream>
 #include <string>
 #include <cmath>
 
 using namespace std ;
 
 string getName ();
 int averageScores( int);
 void printMessage (string, int);
 void tallyScores ( int,int&,int&,int&);
 
  int main()
   {
         const int NUMBER = 4;        // number of scores for each student 
         char moreStudents = 'y';
         string who;                 //name of the student
         int testAverage;
         int students;
         
         cout << "For each student, you will be prompted for a name and "<< NUMBER << " test scores\n" << endl; 
  
         while ( moreStudents =='y' || moreStudents == 'Y'){  
            
            who = getName () ;
            testAverage = averageScores ( NUMBER);
            printMessage ( who, testAverage );       
            cout << "\n\nMore students? Y or N: " ;
            cin >> moreStudents ;
            cout << endl;
            cin.ignore (10, '\n');
            }

      system ("pause");
      return 0;
   }     // end main
   /////////////////////////////////////////////////////////////////////
   // Prompts the user to input the student's name
   string getName ()
   {      
      string name ;
          
      cout << "Enter student name " ;
      getline ( cin, name);
      return name ;
   }       
   /////////////////////////////////////////////////////////////////////////////////////////////////////////////
   // this function inputs and averages scores. Parameter sum adds the scores up.
   
   int  averageScores( int sum )
   {     
      int score1, score2, score3, score4 ;
      int low;
      int rounded;    
      float average; 
      
      cout << "\nEnter four interger scores with a space in between: " ;
      cin >> score1 >> score2 >> score3 >> score4 ;
               
      cout << "\nThe test scores enetered are: " << score1 << " " << score2 << " " <<         score3 << " " << score4 << endl;
               
      sum = score1 + score2 + score3 + score4;
               
      low = score1;
    
      if(low > score2){
	     low = score2;
	     }
		  
      if(low > score3){
		 low = score3;
			
       	 }
	  if(low > score4){
		 low = score4;
			
	     }
	
      cout << "\nThe lowest score of " << low << " is dropped." << endl;
      
      average = (sum - low) / 3.0;
      cout << "\nThe average is " << average << " with three scores and the lowest score dropped." << endl;
      rounded =  static_cast<int>(average + 0.5);
      cout << "\nThis average is then rounded to " << rounded << "." << endl;
      return rounded;
  } // averageScores  /
  
  //////////////////////////////////////////////////////////////////////
  // adds to the appropriate count depeding on the score  
  void tallyScores ( int average, int& repeatIt,int& wow, int& passing)
  {
              				
    if(average <60)
       repeatIt++;
				
    else if(average >= 95)
       wow++;
       
    else if(60 <= average < 95)
       passing++;
    
}
/////////////////////////////////////////////////////
// Prints out a message for the student depending on the score
  void printMessage (string name, int average) 
  {
    string message ;
   	if(average <60)
        message = ("Gotta repeat it");
     
    else if(average >= 95)
		message = ("WOW");

    else if(60 <= average < 95)
        message = ("passing");
    				
    cout <<  "\nAverage for "  <<  name  << " is " << average << "; " << message; 
       
  }          //printMessage

plang007 -5 Junior Poster in Training · Answer 2 · 2011-02-24T09:23:52+00:00

This is my new code, but when I compile it run it, it skips over the line where you have to enter a name. DO you know what to do?

#include<iostream>
 #include <string>
 #include <cmath>
 
 using namespace std ;
 
 string getName ();
 int averageScores( int);
 void printMessage (string, int);
 void tallyScores ( int,int&,int&,int&);
 
  int main()
   {
         const int NUMBER = 4;        // number of scores for each student 
         char moreStudents = 'y';
         string who;                 //name of the student
         int testAverage;
         int students;
         
         cout << "How many students do you want to enter: ";
         cin >> students;
         cout << "\nFor each student, you will be prompted for a name and "<< NUMBER << " test scores\n" << endl; 
  
  
          for (int i = 0; i < students; i++)
          {
           who = getName () ;
            testAverage = averageScores ( NUMBER);
            printMessage ( who, testAverage );       
            cin.ignore (10, '\n');    
           }

         
      system ("pause");
      return 0;
   }     // end main
   /////////////////////////////////////////////////////////////////////
   // Prompts the user to input the student's name
   string getName ()
   {      
      string name ;
          
      cout << "Enter student name " ;
      getline ( cin, name);
      return name ;
   }       
   /////////////////////////////////////////////////////////////////////////////////////////////////////////////
   // this function inputs and averages scores. Parameter sum adds the scores up.
   
   int  averageScores( int sum )
   {     
      int score1, score2, score3, score4 ;
      int low;
      int rounded;    
      float average; 
      
      cout << "\nEnter four interger scores with a space in between: " ;
      cin >> score1 >> score2 >> score3 >> score4 ;
               
      cout << "\nThe test scores enetered are: " << score1 << " " << score2 << " " << score3 << " " << score4 << endl;
               
      sum = score1 + score2 + score3 + score4;
               
      low = score1;
    
      if(low > score2){
	     low = score2;
	     }
		  
      if(low > score3){
		 low = score3;
			
       	 }
	  if(low > score4){
		 low = score4;
			
	     }
	
      cout << "\nThe lowest score of " << low << " is dropped." << endl;
      
      average = (sum - low) / 3.0;
      cout << "\nThe average is " << average << " with three scores and the lowest score dropped." << endl;
      rounded =  static_cast<int>(average + 0.5);
      cout << "\nThis average is then rounded to " << rounded << "." << endl;
      return rounded;
  } // averageScores  /
  
  //////////////////////////////////////////////////////////////////////
  // adds to the appropriate count depeding on the score  
  void tallyScores ( int average, int& repeatIt,int& wow, int& passing)
  {
              				
    if(average <60)
       repeatIt++;
				
    else if(average >= 95)
       wow++;
       
    else if(60 <= average < 95)
       passing++;
    
}
/////////////////////////////////////////////////////
// Prints out a message for the student depending on the score
  void printMessage (string name, int average) 
  {
    string message ;
   	if(average <60)
        message = ("Gotta repeat it");
     
    else if(average >= 95)
		message = ("WOW");

    else if(60 <= average < 95)
        message = ("passing");
    				
    cout <<  "\nAverage for "  <<  name  << " is " << average << "; " << message; 
       
  }          //printMessage

plang007 -5 Junior Poster in Training · Answer 3 · 2011-02-24T09:27:11+00:00

plang007 -5 Junior Poster in Training

15 Years Ago

How would you write that as a while loop?

Saith 74 Junior Poster · Answer 4 · 2011-02-24T09:33:21+00:00

You need to read this thread. It will explain why you are having the error with the string input and it's function.

http://www.daniweb.com/forums/thread90228.html

~~~~~~~~~~~~~~~~~~~~
For the while loop, I just explained it in a very detailed fashion.

~~~~~~~~~~~~~~~~~~~~~
Lastly, check out your expressions such as (60 <= average < 95). You can't do this with the expected results of normal arithmetic. You need to change this to (60 <= average && average < 95)

plang007 -5 Junior Poster in Training · Answer 5 · 2011-02-24T09:43:15+00:00

Nathan, I did what you said but it still skips the line where it asks fo student name, but then that line comes last. like this

Output:

How many students do you want to enter: 4

For each student, you will be prompted for a name and 4 test scores

Enter student name:
Enter four interger scores with a space in between: 99 97 75 86

The test scores enetered are: 99 97 75 86

The lowest score of 75 is dropped.

The average is 94 with three scores and the lowest score dropped.

This average is then rounded to 94.

Average for is 94; passing

Enter student name:

My code.

#include<iostream>
 #include <string>
 #include <cmath>
 
 using namespace std ;
 
 string getName ();
 int averageScores( int);
 void printMessage (string, int);
 void tallyScores ( int,int&,int&,int&);
 
  int main()
   {
         const int NUMBER = 4;        // number of scores for each student 
         char moreStudents = 'y';
         string who;                 //name of the student
         int testAverage;
         int students;
         
         cout << "How many students do you want to enter: ";
         cin.get();
         cout << "\nFor each student, you will be prompted for a name and "<< NUMBER << " test scores\n" << endl; 
  
  
          for(int i = 0; i < students; i++)
          {
           who = getName () ;
            testAverage = averageScores ( NUMBER);
            printMessage ( who, testAverage );       
            cin.ignore (10, '\n');    
           }

     
      system ("pause");
      return 0;
   }     // end main
   /////////////////////////////////////////////////////////////////////
   // Prompts the user to input the student's name
   string getName ()
   {      
      string name ;
          
      cout << "\nEnter student name: " ;
      getline ( cin, name);
      return name ;
   }       
   /////////////////////////////////////////////////////////////////////////////////////////////////////////////
   // this function inputs and averages scores. Parameter sum adds the scores up.
   
   int  averageScores( int sum )
   {     
      int score1, score2, score3, score4 ;
      int low;
      int rounded;    
      float average; 
      
      cout << "\nEnter four interger scores with a space in between: " ;
      cin >> score1 >> score2 >> score3 >> score4 ;
               
      cout << "\nThe test scores enetered are: " << score1 << " " << score2 << " " << score3 << " " << score4 << endl;
               
      sum = score1 + score2 + score3 + score4;
               
      low = score1;
    
      if(low > score2){
	     low = score2;
	     }
		  
      if(low > score3){
		 low = score3;
			
       	 }
	  if(low > score4){
		 low = score4;
			
	     }
	
      cout << "\nThe lowest score of " << low << " is dropped." << endl;
      
      average = (sum - low) / 3.0;
      cout << "\nThe average is " << average << " with three scores and the lowest score dropped." << endl;
      rounded =  static_cast<int>(average + 0.5);
      cout << "\nThis average is then rounded to " << rounded << "." << endl;
      return rounded;
  } // averageScores  /
  
  //////////////////////////////////////////////////////////////////////
  // adds to the appropriate count depeding on the score  
  void tallyScores ( int average, int& repeatIt,int& wow, int& passing)
  {
              				
    if(average <60)
       repeatIt++;
				
    else if(average >= 95)
       wow++;
       
    else if(60 <= average < 95)
       passing++;
    
}
/////////////////////////////////////////////////////
// Prints out a message for the student depending on the score
  void printMessage (string name, int average) 
  {
    string message ;
   	if(average <60)
        message = ("Gotta repeat it");
     
    else if(average >= 95)
		message = ("WOW");

    else if(60 <= average < 95)
        message = ("passing");
    				
    cout <<  "\nAverage for "  <<  name  << " is " << average << "; " << message << endl;
       
  }          //printMessage

NathanOliver 429 Veteran Poster Featured Poster · Answer 6 · 2011-02-24T09:51:22+00:00

I had meant for you to do this

//...
cout << "How many students do you want to enter: ";
cin >> students;
cin.get();  // or cin.ignore (80, '\n');
cout << "\nFor each student, you will be prompted for a name and "<< NUMBER << " test scores\n" << endl; 
/...

C++ loop help

Dani AI

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