Equality and Relational Operators

• = = != //be careful with = =
• < > <= >=
• Boolean expressions: not, and, or
• Precedence revisited

• type name is bool
• Values are true and false
• False is equivalent to a 0
• True is anything but a 0
• both of these sets b2 to false:
  bool b2 = false;
  bool b2 = 0;
• all of these set b1 to true:
  bool b1 = true;
  bool b1 = 1;
  bool b1 = -81;
  bool b1 = 5.6;

Conditional Programming - One-Way ifs

• Not sequential
• When needed to choose between two (or more) alternatives
• One-Way ifsyntax for single statements

if ( condition )
   statement;
• examples of C++ code

if ( input_num < 0 )
      cout << "Error message";
• One-Way if syntax for multiple statements

if ( condition )
{
           statement₁;
           statement₂;
}
• examples of C++ code

if ( grade == 100 )
{
          cout << "Excellent job\n";
          bonus = 1;
}

try some:

• ask user for there 3 exam scores, calculate the average and report if they get above the HIGH_SCORE of 92
• ask the user for 2 numbers and divide them if the second isn't 0

IF-ELSE syntax

• single statements

if ( condition )
     statement;
else
     statement;
• examples of C++ code

if (x < 0 )
     cout << "negative number\n";
else
     cout << "non-negative number\n";
• multiple statements
• examples of C++ code
• used for error checking
• used for alternate selections
• C++ uses short circuit evaluation
• Integers can be used in place of boolean

try some:

• Ask user for a number report if it is even or odd
• Ask the user for there exam score and report if it is passing (60.0 or above) or failing

• More than two possible actions
• Second if can be nested inside of the 1^st "if" part or the 1^st "else" part
• Examples
  
  if ( x <0 )
       cout << "negative number\n";
  else
       if ( x == 0 )
          cout << "zero\n";
  else
         cout << "positive number\n";
   
  ELSE IFs
  
  if (x < 0 )
       cout << "negative number\n";
  else if (x == 0)
       cout << "zero\n";
  else
       cout << "positive number\n";

try some:

• Ask the user for their exam score and report if it is an A (90.0 or above), B, C, D, or F
• Divide two numbers the user enters. If the second number is 0, ask the user to re-input the number and then perform the division.

Characters and Strings

• ASCII

  blank		32
  period		46
  '0'-'9'		48-58
  'A'-'Z'		65-90
  'a'-'z'		97-122
  

• string str1 = "Hello";
  string str2 = "bye"
  if (str1 > str2 )
     cout << String1 os bigger";
  else
     cout <<  "String2 is bigger";
  

• What if str1 is "123" and str2 is "97"?

Examples and Typical Errors

• Errors
  Forgetting braces
  putting ; after ()
  Using = instead of ==
  Redundant testing of boolean values

• Used in place of if-elseif-elseif
• Syntax

switch ( variable)
{
     case1:     statements;
          break;
     case2:     statements;
          break;
     . . .
     casen:     statements;
          break;
     default:     statements;
}

• Create a program that displays a multiple choice question of "How many servings of fruits and vegetables do you get a day?" respond as follows:

  	0  Scurvy and Rickets
  	1 Take lots of vitamins
  	2 You need to eat more fruits and veggies
  	3 Just get one more!
  	4, 5 Good job
  	6 or more -- Over achiever