CS 107 - 6/29/15

for loops - alternative to the while loop.

IN the while loop, we discussed 4 parts


  // intialization
  value = 1;

  while ( value <= 10 )   // condition
    {
      // body statements
      cout << value << endl;

      // increment
      value = value + 1;
    }

The while is really controlled by the three parts of
  1.  the initialization
  2.  the condition
  3.  the increment

However, they really can be all over the place.

The for loop combines these three part together into on line of code.

Syntax:

   for ( <initialization>  ;   <condition>  ;   <increment> )
     {
         <bodyStatements> ;
     }

Rewrite the above while loop as a for loop

  for ( value = 1 ;  value <= 10  ;  value = value + 1 )
     {
        cout << value << endl;
     }

  The <increment> portion of the for loop occurs AFTER
     the <bodyStatements> are executed and before the next
     <condition> is checked


The for loop is covered in Chapter 7.

Also covered in chapter 7 are switch statements and
  do-while loops


   The Switch statement is a alternative for the multiple
    condition if statement


     The switch is restricted to using equality as the
       condition and tends to work best with integers or 
       characters.  (Strings, floating point values tend
       not to work so well.)


    consider the following if statements


    int number;

    cin >> number;


    if ( number == 1 )
      {
        // do this
      }
    else if ( number == 2 )
      {
        // do that 1
      }
    else if ( number == 3 )
      {
        // do that 2
      }
    else if ( number == 4 )
      {
        // do that 3
      }
    else if ( number == 5 )
      {
        // do that 4
      }
    else
      {
        // do some other thing
      }

The above could be rewritten as a Switch statement

   cin >> number;

   switch ( number )
     {
      case  1:  // do this

                break;

      case  2:  // do that 1

                break;  

      case  3:  // do that 2

                break;  

      case  4:  // do that 3

                break;  

      case  5:  // do that 4

                break;  

       default: // do some other thing;

                break;
      }


do-while statement is another form of the while loop


  The while loop checks the condition before the loop body
     is executed for the first time.

      The body of  the while loop can be executed zero or more times

  The do-while loop checks the condition after the loop
     is execute for the first time

      the body of the do-while loop is executed one or more times


  Syntax of the do-while loop

   do 
     {
       <bodyStatements> ;
     }
   while ( <condition> )



Jump to Chapter 11 in Dale book and discuss arrays.


Standard variable store one value per variable name.


Arrays allow multiple values (of the same type) to be stored
  under a single variable name.

  Array use a numeric/integer subscripts to keep track of which
    value is being accessed or modified.

   Creation of an array varaible:

      int arr1[10];

 
   To store a value in an array, the following assignment
     statement would be used:

      arr1[5] = <expr> ;

   To access a value, the "square bracket" notation is again
     used to specify the value being accessed.


      cout << arr1[3];

      int index = 7;

      value1 = arr[index] * 10;


  For an array of size X, the valid subscripts range from
     zero to X-1.

  Code to initialize all 10 positions/indices to 0:
    int arr1[10];

    arr1[0] = 0;
    arr1[1] = 0;
    arr1[2] = 0;
    ...
    arr1[8] = 0;
    arr1[9] = 0;

  Or better yet, use a loop

    int i;

    for ( i = 0 ; i < 10 ; i++ )
      {
        arr1[i] = 0;
      }



When using arrays, we often will use a constant variable.


The C style of create a constant is to use the #define directive


#define ARRSIZE    10

   // The array would be declared as:
   int arr2[ARRSIZE];

   // The array values are initialized as:
   int i;
   for ( i = 0 ; i < ARRSIZE ; i++ )
     {
      arr2[i] = 0;
     }


The C++ style of creating a constant is to use the "const" keyword


   const  int  ARRSIZE = 10;

   // The array would be declared as:
   int arr2[ARRSIZE];

   // The array values are initialized as:
   int i;
   for ( i = 0 ; i < ARRSIZE ; i++ )
     {
      arr2[i] = 0;
     }


Assignment 2 - Mastermind / Code Breaker


  https://en.wikipedia.org/wiki/Mastermind_%28board_game%29


If the code and the guess are each stored in an array



   int code[4];

   int guess[4];

   // to generate the code:
   int i;

   for ( i = 0 ; i < 4 ; i++ )
     {
        code[i] = formula to generate a value from 1 to 6.
     }



   // to determine the number of correct codes in the
   //   correct positions
   int numCorrect = 0;
   int i;

   for ( i = 0 ; i < 4 ; i++ )
     {
       if ( code[i] == guess[i] )
          numCorrect = numCorrect + 1;
     }

   cout << "The number of correct code values in their correct "
        << " positions are: " << numCorrect << endl;


C libray of stdlib has a function called rand()