Executable Statements

• Executable statements take an action.
• We have seen two or three types so far.
• Assignment
  • variable = expression
  • The expression could be constant
  • totalPeople = 4;
  • Or a mathematical expression
  • totalCost = adultCost + otherCost;
  • There are quite a few operators
  • We will discuss these further as we examine different types.
  • In general
    • The expression on the right hand side of the equation is evaluated.
    • The value is stored in the variable on the left hand side of the equation.
• Output
  • cout << expression;
  • cout is a stream.
  • This is for later, but it is a place to put data.
  • << is the stream insertion operator.
    • It evaluates the expression on the right hand side
    • And inserts it into the stream on the left hand side.
    • Stream insertion operators can be stacked

    • cout << "The name is " << name << endl; 

  • endl is a special value
    • It inserts a newline into the stream.
    • It also flushes the buffer.
    • You will see people use '\n' for a new line.
    • Don't use this, use endl
• String +
  • This is called concatenation.
  • It appends one string or character to the end of another.
  • And returns a string.
  • Strings can be literal or stored in a variable.

  • string firstName,
           lastName,
           fullName;
    
    firstName = "Dan";
    lastName = "Bennett";
    fullName = firstName + " " + lastName; 

• Including the quotation character in a string
  • The quote character " is used to mark literal strings.
  • If we want it to be part of a string, we need to escape it with a \
  • word = "\"Hello\" World";
• Reading in strings.
  • Reading in strings with no spaces
    • cin is an input stream.
    • >> is the stream extraction operator.

    • string word;
      cin >> word; 

      • Skips all whitespace
      • reads in non-white space characters and stores them in word
      • stops when a whitespace character is encountered.
  • Reading ins strings with spaces
    • getline is a function
      • It takes
        • an input stream
        • a string variable.

          • string phrase;
            getline(cin, phrase); 

          • It reads all characters, including whitespace, from the stream until the newline character is reached.
          • It stores these characters in the string.
          • It stops at the new line, removing it from the stream but adding it to the string.
      • Mixing getline and stream extraction operators
        • This code has a problem.

          string word, phrase;
          
          cout << "Enter a word: ";
          cin >> word;
          cout << "Enter a phrase: ";
          getline(cin, phrase); 

        • You would expect it to read a word then a phrase.
        • Unfortunately what will happen is that it will read a word and a blank line.
        • Consider the stream

          hello↩
          This is a phrase ↩ 

        • What would happen is hello would be stored in word.
        • Then it would stop.
        • The getline would read the newline character and the empty string would be stored in phrase.
      • To fix this do the following:

        string word, phrase;
        
        cout << "Enter a word: ";
        cin >> word;
        cin.ignore(100,'\n');
        cout << "Enter a phrase: ";
        getline(cin, phrase); 

      • ignore will skip the next 100 characters or until it sees a newline character.
    • Some other special characters
      • Anything single thing inside ' ' is a character.
      • Look at the ascii table.
      • '\t' is the tab.
      • '\n' is the newline character.