CS 107 - 6/22/15


Lecture Quiz 3 Questions
  // Q 1
  int x, y, z;

  x = 10;
  y = 5;

  z = x * 2 + 3 * y;

  cout << "Q1: The value in z is: " << z << endl;

  // Q 2
  int x, y, z;

  x = 10;
  y = 5;

  z = x + 2 * 3 + y;

  cout << "Q2: The value in z is: " << z << endl;

  // Q 3
  int x, y, z;

  x = 6;
  y = 2;

  z = x * 2 + 3 * y;

  x = 3;
  y = 4;
  cout << "Q3: The value in z is: " << z << endl;



Consider the following assignment statement;

  int val = 10;

  val = val + 1;

C/C++ have the following short-cut statements

      val += 1;     
Is the same as:
      val = val + 1;


   ++, --   which increment or decrement a value by 1



    val++;
is the same as:
    val = val + 1;


    val--;
is the same as:
    val = val - 1;



  Note that these operators can be used in either the
      prefix format or the postfix format.

   Prefix:    ++val;
   Postfix:   val++;


This is getting clever; DON'T DO THIS
    a = b++ + --c;


   val = 5;
   val = val++;   // does not produce the intended results

The proper code should be:
   val = 5;
   val++;



Input and Output

    Standard Input Stream (from the keyboard) is:  cin

    Standard Output Stream (to to terminal) is: cout


    cout << "Hello There"  << endl;

The use of cin and cout require the iostream library to be
   included by the preprocessor directive of:

#include <iostream>


To read in a value from the keyboard we use the following:

    int val;

    cin >> val;

    string planet;


    cin >> planet;




If Statements / Selection Statements

Chpater 5


The "Flow of Control" so far has been sequential statements

When using Selection Statements, the program can "select"
  whether it will executed a block of statements or not.


Boolean Variables/expressions

   a Boolean variable/expression can have a value of
     true or false

   bool finished;


   finished = false;

The above shows the use of Boolean varaibles; however, these
  are rarely used.

The most common way of using boolean expression is through the
   relational operators


   ==      equality   (equals)
   !=      inequality (not equals)
   <       less than
   <=      less than or equal to
   >       greater than
   >=      greater than or equal to



      example

           val >= 10

      The above evaluates to either true or false depending on
         the current value of the variable val


The syntax of the simplest form of the if statement is:

    if (  <booleanExpression>  )
      {
         <trueBlock> ;
      }


  The statement(s) in the <trueBlock> are only executed if
    the <booleanExpression> evaulates to true


   int number1;

   cin >> number1;


   // get the absolute value of what the user entered
   if ( number1 < 0 )
     {
        number1 = 0 - number1 ;
     }

   cout << "The absolute value is: " << number1 << endl;


The above code without the curly brackets:

   if ( number1 < 0 )
     number1 = 0 - number1 ;

When written with out curly brackets, we can accidently introduce
  errors by adding in extra lines and forgetting to add in the
  curly brackets.  The following shows this error:
   if ( number1 < 0 )
     cout << "Performing the absolute value operation" << endl;
     number1 = 0 - number1 ;

The solution is to add the curly brackets:

   if ( number1 < 0 )
   {
     cout << "Performing the absolute value operation" << endl;
     number1 = 0 - number1 ;
   }


Another (more common) version of the if statement is the
  "if-then-else" statement

   Syntax:

     if (  <booleanExpression>  )
       {
         <trueBlock> ;
       }
     else
       {
          <falseBlock> ;
       }


  If the <booleanExpression> evaluates to true, the <trueBlock>
     is executed.
  Otherwise (if the <booleanExpression> evaluates to false),
     the <falseBlock> is executed.

Example:  determine the greater of two values


   int val1, val2;
   int maxValue;


   cin >> val1;
   cin >> val2;

   if ( val1 >= val2 )
     {
       maxValue = val1;
     }
   else
     {
       maxValue = val2;
     }

  cout << "The larger value is: << maxValue << endl;


When we have a larger number of optional blocks of code, 
we can chain if statements together.  Where the next if
statement if the <falseBlock> of the previous if statement.


    int average;
    char grade;


    cin >> average;


    if ( average >= 90 )
      {
        grade = 'A';
      }
    else if ( average >= 80 )
      {
        grade = 'B';
      }
    else if ( average >= 70 )
      {
        grade = 'C';
      }
    else if ( average >= 60 )
      {
        grade = 'D';
      }
    else 
      {
        grade = 'F';
      }

   cout << "The final grade is: " << grade << endl;