If you are new to programming or just a beginner you might find it hard to understand the concept of control statements, especially while working with the QBASIC programming language.

QBASIC is a beginner-friendly easy-to-learn programming language that allows you to write programs that can be executed on a computer. And one of the fundamental concepts you will learn about programming is about the control statement. So, in this article, we will understand QBASIC control statements and their syntax with the help of examples.

What are Control Statements in QBASIC?

The control statements are those statements that control the flow of execution of commands in a program. It helps us to execute certain statements based on specific conditions till the specific condition is met.

In QBASIC sometimes the user might want to change the order of execution of code, either by repeating or by skipping the executions of a few statements based on a given condition. In such cases, you have to use the control statements as they have the capability to make certain decisions in the run time of the code. Examples of control statements in QBASIC (QB64) are GOTO, IF THEN, IF THEN ELSE, END IF, etc.

Types of Control Statements

The control statement can be classified into three main types:

1. Conditional Statements

It enables you to execute a set of statements based on a particular condition. Examples of conditional statements are: IF-THEN, IF-THEN_ELSE, and SELECT CASE

2. Loop Statements

These statements enable you to repeat a set of statements until a specific condition is met. Examples of loop statements are: DO LOOP and FOR NEXT.

Learn more about Looping Statements in QBasic

3. Unconditional Statement

This statement executes regardless of whether a condition is true or false. It transfers the flow of the execution from one statement line to another statement. The GOTO statement is the only unconditional statement in QBASIC programming.

Here’s a table repesentation of the control statements in QBasic.

Conditional Statements	Looping Statements	Unconditional Statement
IF THEN	DO LOOP	GOTO
IF THEN ELSE	FOR NEXT
IF THEN ELSEIF
SELECT CASE

Control Statements In QBASIC (QB64)

Here are some of the examples of control statements in QBASIC with syntax and examples.

Conditional Statement with example

IF THEN statement

It is the most basic control statement in Qbasic. It is used to make decisions based on comparisons. Here it checks if the condition is True, if yes, then it executes the THEN statement.

Syntax:

IF [conditional expression] THEN  

[statement]

END IF

Example:

CLS
INPUT "Type YES to print 1 to 4"; Y$
IF Y$ = "YES" THEN
PRINT "1"
PRINT "2"
PRINT "3"
PRINT "4"
ENDIF
END

ENDIF statement is used when we have multiple IF statement in the program. We have to use the ENDIF before the END statement.

IF THEN ELSE Statement

The IF THEN ELSE statement is a decision-making control statement. If the given IF condition is True then the THEN statement will execute or else the ELSE statement is executed.

Syntax:

IF [conditional expression] THEN

[statement 1]

ELSE

[statement 2]

END IF

Example:

CLS
INPUT "Enter a number"; N
IF N > 10 THEN
PRINT "The entered number is greater then 10"
ELSE
PRINT "The number is smaller then 10"
END IF
END

IF THEN ELSEIF statement

It is similar to the IF THEN ELSE statement, but the difference is that in IF THEN statement we could only test one IF condition, and with the help of the IF THEN ELSEIF statement we can use multiple IF conditions in the same program.

Syntax:

IF [condition] THEN

[statement 1]

ELSEIF

[statement 2]

ELSE

[statement n]

END IF END

Example:

CLS
N = 10
IF (N = 5) THEN
  PRINT "The first statement is true"
ELSE IF (N = 10) THEN
  PRINT "The second statement is true"
ELSE 
  PRINT "Both statements false"
END IF
END

SELECT CASE Statement

The SELECT CASE statement enables you to execute a set of statements based on the value of the expression. It’s similar to IF THEN statement but much easy to understand and concise.

Syntax:

SELECT CASE expression
  CASE value1
    'Statements to execute if expression = value1
  CASE value2
    ' Statements to execute if expression = value2
  CASE ELSE
    ' Statements to execute if expression does not match any of the above cases
END SELECT

Example:

CLS
INPUT "ENTER NUMBER BETWEEN 1 TO 4"; N
SELECT CASE N
CASE 1
    PRINT "You are level 1" 
CASE 2
    PRINT "You are level 2"
CASE 3
    PRINT "You are level 3"
CASE 4
    PRINT "You are level 4"
END SELECT          

Looping Statement with example

Looping statements are those control statement that enables you to repeat a set of statements until the condition is met.

DO LOOP statement

The DO LOOP is also known as the DO WHILE LOOP and it is used to execute a set of instructions within a loop if the comparison is True.

Syntax:

DO

[statement]

LOOP WHILE END

Example:

CLS
N = 1
DO
    PRINT N
    N = N+1
LOOP WHILE N <=10
END

This program will print out natural numbers from 1 to 10.

FOR NEXT Statement

The FOR NEXT statement is used to execute a set of instructions for a certain amount of times.

Syntax:

FOR counter = [initial value] TO [final value]

[statement]

NEXT counter

Example:

CLS
FOR n = 1 TO 5
    PRINT n
NEXT n
END

This will print numbers from 1 to 5.

Unconditional Statement with Example

GOTO Statement

The GOTO statement is the only unconditional statement in QBASIC programming language. It
is used to transfer the execution flow of a program statement from one line to another.

Syntax:

GOTO [label/ line]

Example:

CLS
INPUT "Enter your mark:"; N
IF N >= 30 THEN GOTO P
IF N < 30 THEN GOTO F
P: 
    PRINT "You passed your exam"
END
F: 
  PRINT "You failed your exam"    
END

Here, the GOTO statement along with the IF THEN statement execute a specific line depending on the condition of the IF condition.

Conclusion:

In this article, we have discussed the control statements in QBASIC and how we can use them to control the flow of execution in a program.

We have learned about conditional statements (IF…THEN…ELSE, SELECT CASE), looping statements (DO…LOOP WHILE, FOR…NEXT, WHILE…WEND), and unconditional statements (GOTO).

You can easily understand the use of all three main control statements by looking at their syntax and examples.

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