Using Booleans in VEXcode Pro V5

The “bool” data type generates logically true or false.

Logical/Boolean Operators

Logical/Boolean Expressions

if(<boolean expressions>)
	{
	.....<block>
	}

The <boolean expressions> will contain a single or complex expression to be evaluated. The <block> means a block of code that will be executed only if the <boolean expressions> are evaluated to be true.

More Boolean Expressions:

Boolean Expression	What it means
if (x == 10)	if x is equal to 10
if (x <= 10)	if x is less than and equal to 10
if (x > 10 || y > 20)	if x is greater than 10 or y is greater than 20
if (x <= 10 && y <= 20)	if x<=10 and y<=20
if !(x > 10 || y > 20)	if x<=10  and y<=20
if ( !( x <=10 || x >=20) )	If x>10 and x<20

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Use special caution when using boolean expressions!

A Boolean type (bool) is a simple integer value.

Let’s take a look at how if (... ) is interpreted:

• if (...) will be computed by the compiler; it produces a meaning of true or false.
• Truth is: when ( ... ) produces anything other than 0 (i.e. zero), the if ( .... ) will mean true.
• So: the following expressions are always true:
  • if (1)
  • if ( 10 )
  • if ( anything results non-zero)

   

Common Errors you must pay attention to:

Example 1:

int X = 10, Y=20;
if  (X = Y)
	brain.Screen.print("X and Y are the same.”);   
else
	brain.Screen.print("X and Y are different.”);

Output: X and Y are the same. 

Why?

if (X = Y) really means:

• Assign Y to X, so X has value of 20 
• The compiler interprets it as if (20) where (20) is true as it is not (0).

Example 2:

int X = 0, Y=0;
if  (X = Y)
	brain.Screen.print("X and Y are the same.”);   
else
	brain.Screen.print("X and Y are different.”);

Output: X and Y are different. 

Why?

if (X = Y) really means:

• Assign Y to X, so X has value of 0 (zero).
• Compiler interprets it as: (0) as false.