If
The If statement evaluates a relational expression. If the expression is true, it follows the THEN path and executes one or more specified statements or transfers control to another line, as indicated in the instructions. If it is false, it follows the ELSE path, which may specify another statement, transfer control to another line, or initiate another IF statement.
For example, suppose that the passing grade on an exam is 60. The BR statement below determines whether the condition grade >= 60 is true or false. If the condition is true, "Passed" is displayed, and the next BR statement in order is performed. If the condition is false, the output statement is ignored, and the next BR statement in order is performed.
00010 print "Enter a grade" 00020 input grade 00030 if grade >= 60 then print "Passed" 00040 stop
Syntax
Multi-line IF Statements
The same program could be rewritten to put the print "Passed" statement on a separate line with indentation to emphasize that this statement may or may not happen:
00010 print "Enter a grade" 00020 input grade 00030 if grade >= 60 then 00040 print "Passed" 00050 end if 00060 stop
In the above example, end if marks the end of the statements which will be performed if the grade >= 60 condition is true. The indentation of line 40 of this selection statement is optional, but recommended, because it emphasizes the inherent structure of the if statement.
Below is the general syntax used in a multi-line if statement:
IF condition THEN [body] END IF
The optional body between IF condition THEN and END IF is a group of zero or more statements. At least one statement in the body is encouraged for clarity.
Although it is not required to indent the body of a multi-line IF statement, it is highly recommended to indent it for readability.
Programmers often run into situations in which more than one statement needs to be executed if a particular condition is true. To illustrate the method of achieving this in BR, we will expand the above example to print multiple statements if the grade entered by the user is more than or equal to 60:
00010 print "Enter a grade" 00020 input grade 00030 if grade >= 60 then 00040 print "Passed" 00050 print "You will not need to re-take the test" 00060 print "Good job" 00070 end if 00080 stop
IF... ELSE Statement
When your programming needs call for two different actions depending on whether or not a condition is true, the IF... ELSE statement should be used.
00010 print "Enter a grade" 00020 input grade 00030 if grade >= 60 then 00040 print "Passed" 00050 else 00060 print "Failed" 00070 end if 00080 stop
IF... ELSE IF Statement
When your programming needs call for many different actions depending on multiple conditions, the IF... ELSE IF statement should be used.
00010 print "Enter a grade" 00020 input grade 00030 if grade >= 90 AND grade <= 100 then 00040 print "Got an A" 00050 else if grade >= 80 AND grade <= 89 then 00060 print "Got a B" 00070 else if grade >= 70 AND grade <= 79 then 00080 print "Got a C" 00090 else if grade >= 60 AND grade <= 69 then 00100 print "Got a D" 00110 else if grade < 60 AND grade > 0 then 00120 print "Failed" 00130 end if 00140 stop
IF... ELSE IF... ELSE Statement
The program above covers all scenarios except two:
1. When the grade entered by the user is negative 2. When the grade entered by the user is greater than 100
In order to catch this problem, you may add an ELSE clause to the end of the program above, resulting in:
00010 print "Enter a grade" 00020 input grade 00030 if grade >= 90 AND grade <= 100 then 00040 print "Got an A" 00050 else if grade >= 80 AND grade <= 89 then 00060 print "Got a B" 00070 else if grade >= 70 AND grade <= 79 then 00080 print "Got a C" 00090 else if grade >= 60 AND grade <= 69 then 00100 print "Got a D" 00110 else if grade < 60 AND grade > 0 then 00120 print "Failed" 00130 else 00140 print "Invalid grade. Must be positive and less than 100" 00150 end if 00160 stop
Complex Conditions
Often in programs, the execution of a statement depends on several different conditions. For example, you may want REQUIRE the user to enter a name, a date of birth, and a social security number before saving a record.
00010 dim name$*40, dob$*8, ssn$*9 00020 get_data:! 00030 input name$, dob$, ssn$ 00040 if trim$(name$)="" or trim$(dob$)="" or trim$(ssn$)="" then 00050 print "Enter ALL THREE fields before saving" 00060 goto get_data$ 00070 end if
To see more information on operations see Operations.
Nested if statements
Sometimes you may need to embed if statements into other if statements. These embedded if statements are formerly known as nested if statements. Below is an example:
00020 PRINT "Enter employee type" 00030 PRINT "1 - Manager" 00040 PRINT "2 - Hourly" 00050 PRINT "3 - Commission" 00060 INPUT PAYCODE 00070 IF PAYCODE = 1 THEN ! Manager 00080 PRINT "Manager Selected." 00090 PRINT "Enter Weekly Salary " 00100 INPUT SALARY 00110 if salary => 0 then 00120 PRINT "Manager's pay is " & STR$(SALARY) 00130 else 00140 print "Can't have a negative salary" 00150 end if 00160 ELSE IF PAYCODE = 2 THEN ! Hourly Worker 00170 PRINT "Hourly worker Selected." 00180 PRINT "Enter the hourly salary " 00190 INPUT WAGE 00200 PRINT "Enter the total hours worked " 00210 INPUT HOURS 00220 if hours < 0 then 00230 print "Can't have negative hours" 00240 else if HOURS <= 40 THEN 00250 LET SALARY = HOURS * WAGE 00260 ELSE 00270 LET SALARY = 40.0 * WAGE + ( HOURS - 40 ) * WAGE * 1.5 00280 END IF 00290 PRINT "Hourly worker's pay is " & STR$(SALARY) 00300 ELSE IF PAYCODE = 3 THEN ! Commission Worker 00310 PRINT "Commission Worker Selected." 00320 PRINT "Enter gross weekly sales " 00330 INPUT SALES 00340 if sales > 0 then 00350 LET SALARY = SALES * .057 + 250 00360 PRINT "Commission worker's pay is " & STR$(SALARY) 00370 else 00380 print "Can't have negative sales" 00390 end if 00400 END IF
If there are several levels of indentation, each level should be indented the same additional amount of space.