Strings Expressions

• assignment:

• string myname;
  
  myname = "Dan";
     

• Concatenation (putting two strings together)

• string firstname;
  string lastname;
  string fullname;
  
  firstname = "Dan";
  lastname = "Bennett";
  fullname = firstname + " " + lastname;
     

Output

• cout is the standard output stream.
  • Standard - it is set up for us by the os without us asking for it.
  • Stream - data flows out of your program.
  • Insertion Operator
    • << is called the insertion operator.
    • << is also called ``put to''
    • Takes two arguments.
      • LHS a stream to put it into
      • RHS an expression to output
      • Examples

        cout << "Hello";
        cout << "Hello" + " " + "World";
        cout << avar;
        	   

    • You can use multiple of this is an output statement
      • It returns the stream it put to
      • Examples:

        cout << "Hello" << "World";
        cout << avar << "Is less than " << bvar;
        	   

• endl
  • Endl serves two functions
    • It outputs an end of line marker (new line)
    • It flushes the buffer.
  • Example:

    cout << "We will now print three blank lines" << endl;
    cout << endl << endl << endl;
    cout <<"Those were three blank lines";
           

Some Odds and Ends

• A " in a string
  • To put a " in a string, escape it with /"
  • Example:

    cout << "He said \"Hello\"" << endl;
            

• Comments can be inside of /* */ pairs
  • Begun with /*
  • Ended with the first */
  • Can cross multiple lines
  • Example:

    /********************************************************
    *   Program 1:   A program to do something              *
    *   Programmer:  Dan Bennett                            *
    *   Date Due:  9 Sep 2001                               *
    ********************************************************/
    
    /* this is the program */
    /* It does something
         but not on this line */
    	 

The structure of a program

• Please consider the following program

  /************************************************************
  *   Program 1, a program to construct username and password *
  *   Programmer  Dan Bennett                                 *
  *                                                           *
  *   This program will output a username and password        *
  ************************************************************/
  
  #include <iostream>
  #include <string>
  
  const char first_initial ='d';  // the first initial of the first name
  const char last_initial ='b';   // the first initial of the last name
  const string  idno = "345678";       // The banner id (last six digits only)
  const string  month = "07";          // Month the person was born
  const string  day = "04";            // The day the person was born
  const string  year = "76";           // Last two digits of the year of birth
  
  int main () {
      string username;  // the constructed user name
      string passwd;    // the constructed password
  
      // build the username
  
      username = first_initial + idno + last_initial;
  
      // build the password
  
      passwd = month + day + year;
  
      // output the results
  
      cout << "The username is "<< username << endl;
      cout << "The password is "<< passwd << endl;
  
      return(0);
  }
      

• Note
  1. Comments
  2. Compiler directives (#include statements)
     • These are not part of C++
     • They don't end with a ;
     • They are used by a program called a pre-processor
     • Don't worry about them now.
  3. Constant declarations
  4. Main routine
     1. Variable declarations
     2. executable statements
     3. return