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Logical Operators

 

Run your mouse over the panel at the left to see information about the logical operators.

 

A single comparison in an if statement often is not enough to determine whether data matches your criteria.  For example, you may need to check to see if a user enters a number within a certain range.  To accomplish this task, you will need the logical operators in your if statement. 

These logical operators which result in a TRUE/FALSE condition are also referred to as Boolean Operators.

It's time to remember those truth tables from Mathematics!  Yeek!!

 
 && (AND)
   (3 + 2 = 5) && (6 + 2 = 8)   TRUE
   (4 + 3 = 9) && (3 + 3 = 6)   FALSE
 | | (OR)   found above the backslash on the keyboard
   (3 + 6 = 2) || (4 + 1 = 5)      TRUE
   (1 + 1 = 3) || (3 + 3 = 9)      FALSE
 ! (NOT)
   !(4 + 3 = 5)      TRUE

 

BEWARE:
Math:             2 < x < 10    OK
Computer:    if (2 < x < 10)   NO!!! 
    
The computer will only check the first condition 2 < x.
              if ((2 < x) && (x < 10))  YES

 

Remember DeMorgan's Laws:

Mathematical Version: Programming Version:
Equivalent statements:
if (!(num >= 0 && num <= 65))
if (num < 0 || num > 65)

 

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