Copyright © 1997, 1999, 2008
Robert W. Hasker

Transition

• (Review:) Ch. 3: expressions, functions
• Ch. 4: input

Discuss:

• cin.get()
• cin.ignore()

Input Details

• input by <<
  • The >> is meant to suggest data is being transferred from the input into the variable.
  • type of variable determines what is read (int, float, char)
  • when read data using >>, C++ skips any whitespace (spaces, tabs, newlines)
• Example: program to read three scores (integers) and print their average:
  • Algorithm [have them write it!]

    	1. read the scores using cin
    	2. compute the average (what type?)
    	3. print the result
    

  • Solution:

    	#include <iostream>
            using namespace std;
    
    	const int NUM_SCORES = 3;
    
    	int main()
    	{
    	   int score1, score2, score3;
    	   float average;
    	   cout << "Enter the 3 scores separated by spaces: ";
    	   cin >> score1 >> score2 >> score3;
    	   average = float(score1 + score2 + score3) / float(NUM_SCORES);
    	   cout << "The average is " << average << endl;
    	   return 0;
    	}
    

More on Reading Data

• operator>> skips whitespace; what if whitespace is significant?
• example: read answers (letters) to quiz, use space if user didn't answer
  • assume 4 questions
  • "summarize" answers by printing them on a line (can redirect output to file, score file)
  • will talk later about how to score results
  • first attempt:

    	char ans1, ans2, ans3, ans4;
    	cin >> ans1 >> ans2 >> ans3 >> ans4;
    

    problem: skips spaces
  • solution: use cin.get: operation to read single character from input

    	cin.get(ans1);
    	cin.get(ans2);
    	cin.get(ans3);
    	cin.get(ans4);
    

• issue: how do we skip the rest of the stuff on a line?
• example: form contains user id (a long integer) and name; we just need id
  • introduce long
  • attempt:

    	long id;
    	??? name;
    
    	cin >> id >> name;
    

  • solution: use cin.ignore
    • skips all characters up to (but not including) given char
    • to skip to end of line:

      	cin.ignore('\n');
      

  • application:

    	long id;
    
    	cin >> id;
    	cin.ignore('\n');
    

Review

• input using >>
• prompt
• get
• ignore