If Else

• This is the first of two forms of the if statement.
• The syntax of the if else statement is

• if (boolean expression) then-Statement else else-Statement
      

• The symantics of the if else statement are
  • Evaluate the boolean expression
  • If it (the boolean expression) evaluates to true
    • Execute the then-Statement
    • Exit the control structure
  • If it (the boolean expression) evaluates to false
    • Execute the else-Statement
    • Exit the control structure.
• I feel, for the most part, it is bad form to use the if-else statement in the default form, so I almost always add code blocks.

  • if (boolean expression) {
       statements;
    } else {
       statements;
    }
        

  • You see this in all variations of {} allignment:

  • if (boolean expression) 
    {
       statements;
    } 
    else 
    {
       statements;
    }
        

  • I really dislike this, it follows the pattern, but takes up much more space.

  • if (boolean expression) {
       statements;
    } 
    else {
       statements;
    }
        

  • Don't like this either, it is inconsistant with how they do functions.
  • So just pick a style and be consistant.
• Printing the value of a boolean

  • bool flag;
    
    if (flag == true) {
        cout << "true"; 
    } else {
        cout << "false"; 
    }
    	 

  • Be careful, if you mess this up you will have a problem:

  • bool flag;
    
    if (flag = true) {
        cout << "true"; 
    } else {
        cout << "false"; 
    }
    	 

  • Will always print "true", why?

  • bool flag;
    
    if (true == flag) {
        cout << "true"; 
    } else {
        cout << "false"; 
    }
    	 

  • Would be better, and I would like to do this, but I can't seem to adjust to it.

  • bool flag;
    
    if (flag) {
        cout << "true"; 
    } else {
        cout << "false"; 
    }
    	 

  • Is actually what I prefer.
• Some simple programs:
  • Write a program which prints the word "true" if a boolean value is true and "false" if it is not. (printTF.C)
  • Write a program which reads a person's hourly wage and the number of hours they work each week and determines if they are above or below the Federal Poverty Level. (poverty.C)