The If statement.

• Used to make decisions.
• Syntax

  if (boolean expression) {
     statement;
  }
     

• Example:

• 
  cout << "Enter the hours worked " ;
  cin >> hours;
  cout << "You entered " << hours << " hours" << endl;
  if (hours >= 40) {
     cout << "You worked overtime ";
     overtime = hours - 40;
  }
  
     

The If then else statement

• Syntax

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

• Example

  
     if (hours > 40 ) {
        cout << "You worked overtime" << endl;
        overtime = hours - 40;
     } else {
        cout << "You didn't work overtime " << endl;
        overtime = 0;
     }
     

General Notes

• The {}
  • Unnecessary if there is a single statement

  • 
    if (hours > 40) 
       overtime = hours - 40;
    
          

  • But put them anyway.
  • They help avoid confusion later.
• Indentation
  • Not required by the compiler.
  • Absolutley required by me.
• See page 233
• A very bad, but really common mistake

  • 
    x = 4;
    if (x = 7) {
       cout << "X is seven" << endl;
    }
          
          

  • How do you avoid this?
    • reverse the comparison

    • 
      x = 4;
      if (7 = x) {
         cout << "X is seven" << endl;
      }
      	 

    • watch for it when it occurs.
• A debugging note.
  • Add output statements to each case

  • 
    if (condition) {
        cout << "DEBUG I am in the THEN part " << endl;
        other statements
    } else {
        cout << "DEBUG I am in the ELSE part " << endl;
        other statements
    }
          

Some things to try

• Enter an amount and a price, tell if the amount is sufficient, give the correct change, tell amount short.
• Enter a salary and determine the tax rate.

  Salary	Rate
  < 10,000	0%
  10,001 < S < 20,000	7%
  20,001 < S < 30,000	9%
  30,001 < S < 40,000	12%
  40,001 < S	15%