Assignment Operations: Difference between revisions
(edit) |
(edit) |
||
| Line 26: | Line 26: | ||
'''Note''' that when this assignment operator is used in any expression (for example: in the condition of an [[IF]] [[THEN]] statement), parentheses must be used to clarify the order of execution Otherwise, unexpected results may occur. | '''Note''' that when this assignment operator is used in any expression (for example: in the condition of an [[IF]] [[THEN]] statement), parentheses must be used to clarify the order of execution Otherwise, unexpected results may occur. | ||
'''IMPORTANT NOTE:''' when the equal sign is used in an [[If]] [[statement]], it is '''NOT''' used for assignment. Instead, it is used for '''comparison'''. Consider the example below: | '''IMPORTANT NOTE:''' when the equal sign is used in an [[If]] [[statement]], it is '''NOT''' used for assignment. Instead, it is used for '''comparison'''. Consider the example below: | ||
| Line 34: | Line 35: | ||
In the above example, assignment DOES NOT takes place, instead the IF statement evaluates to FALSE and the '''print''' statement DOES NOT execute. | In the above example, assignment DOES NOT takes place, instead the IF statement evaluates to FALSE and the '''print''' statement DOES NOT execute. | ||
'''IMPORTANT NOTE:''' when the equal sign is used in an [[If]] [[statement]], it is equivalent to using two equal signs '''=='''. So the above example is identical in effect to the one below: | '''IMPORTANT NOTE:''' when the equal sign is used in an [[If]] [[statement]], it is equivalent to using two equal signs '''=='''. So the above example is identical in effect to the one below: | ||
| Line 42: | Line 44: | ||
For clarity, it may be better to use '''==''' for comparison. | For clarity, it may be better to use '''==''' for comparison. | ||
'''IMPORTANT NOTE:''' when the '''forced assignment operator :=''' is used in an [[If]] [[statement]], it is used for '''forced assignment, not for comparison.''' Consider the example below: | '''IMPORTANT NOTE:''' when the '''forced assignment operator :=''' is used in an [[If]] [[statement]], it is used for '''forced assignment, not for comparison.''' Consider the example below: | ||
Revision as of 17:28, 10 January 2012
There are two assignment operators in BR: the equal sign =, which denotes regular assignment, and the colon-equal sign :=, which denotes forced assignment,
They are similar in how they work with a slight difference.
Both of them are Binary operators, which means they take two arguments - one on the left, and another one on the right.
Numeric and String variables both may be used with regular and forced assignment operators.
Regular Assignment
The equal sign = simply makes the variable on the left side of it equal to the value on the right side of it. The example below assigns the value of 5 to the variable x:
00010 let x = 5 ! correct
Note that you cannot do the reverse. The example below will result in an error.
00010 let 5 = x ! incorrect
The disadvantage of the equal sign assignment operator = is that it may only be used as a separate statement.
Forced Assignment
If your programming needs call for multiple operations in one statement, you may use the forced assignment operator :=. The example below assigns the value of 5 to x and then compares the value of x (which is now 5) to the value of 2:
00010 if (x:=5) > 2 then print "The forced-assigned value is larger than 2"
Note that when this assignment operator is used in any expression (for example: in the condition of an IF THEN statement), parentheses must be used to clarify the order of execution Otherwise, unexpected results may occur.
IMPORTANT NOTE: when the equal sign is used in an If statement, it is NOT used for assignment. Instead, it is used for comparison. Consider the example below:
00010 let x = 1 ! assignment takes place 00020 let y = 1000 ! assignment takes place 00030 if x = y then print "1 is equal to 1000" ! assignment DOES NOT takes place
In the above example, assignment DOES NOT takes place, instead the IF statement evaluates to FALSE and the print statement DOES NOT execute.
IMPORTANT NOTE: when the equal sign is used in an If statement, it is equivalent to using two equal signs ==. So the above example is identical in effect to the one below:
00010 let x = 1 ! assignment takes place 00020 let y = 1000 ! assignment takes place 00030 if x == y then print "1 is equal to 1000" ! assignment DOES NOT takes place
For clarity, it may be better to use == for comparison.
IMPORTANT NOTE: when the forced assignment operator := is used in an If statement, it is used for forced assignment, not for comparison. Consider the example below:
00010 let x = 1 00020 if x:=2 then print "forced assignment as a condition of an if statement always evaluates to true"