Qbasic Looping statements with Examples

Qbasic is an easy-to-learn programming language, especially for beginners. It provides a wide range of features and functionalities that can make learning a programming language fun and enjoyable. And one of the features that is important in any programming language is the use of looping statements.

In this article, we will understand one of the control statements i.e the looping statement in QBASIC programming. You will learn about different looping statements with it’s syntax and examples.

Read about QBasic Control Statement with Examples

What is a Looping Statement in QBASIC?

In any programming language loop is an important concept. It is a process where we have to repeat a task multiple times until the given condition becomes true. And to perform the loop operation QBASIC provides us with different looping statements like FOR..NEXT, DO LOOP, WHILE WEND, etc.

So by definition, a looping statement in QBASIC is a statement that helps us to loop or repeat a task multiple times until the given condition is True. Using a looping statement we can execute a statement (or a group of statements) many times until it fulfills a given condition.

There are four types of looping statements in QBasic:

Looping Statement	Description
FOR…NEXT	Repeats a block of statements for a specific number of times, using a counter variable to keep track of the number of times the loop has been executed.
DO…LOOP	Repeats a block of statements while a specific condition is true. The block of code is executed at least once, regardless of whether the condition is true or false.
WHILE…WEND	Repeats a block of statements while a specific condition is true. The block of code is executed only if the condition is true.
NESTED FOR…NEXT	Repeat a block of statements with two FOR NEXT loops, where one is looped inside the first FOR NEXT loop.

Let’s understand it better with some examples:

FOR NEXT Looping statement

The FOR NEXT loop is used to repeat a group of statements for a specific number of times. It uses a counter variable to keep track of the number of times the loop has been executed.

A counter is a variable that counts the iteration of a loop in a program. It needs two values :

An initial value, and

An incremented value

Syntax:

FOR [counter] = [initial] TO [end value] STEP [stepvalue]

[statements]

NEXT [counter] END

Example 1: Print the natural numbers from 1 to 10 in QBASIC

CLS
FOR num = 1 TO 10
    PRINT num;
NEXT num
END

Example 2: Write a QBASIC program to find the sum of all even numbers from 1 to 20 (Using STEP)

CLS
sum = 0
FOR i = 2 TO 20 STEP 2                
  sum = sum + i 
NEXT i
PRINT "Sum of even numbers from 1 to 20 ="; sum

DO LOOP looping statement

The DO..LOOP statement repeats a group of statements/codes while a particular condition is True. It is generally preferred when the number of iterations is not known beforehand.

The DO…LOOP statements are of two types:

DO WHILE
DO UNTIL

DO WHILE loop

The DO WHILE loop executes a code as long as the specified condition is True. The DO WHILE loop first executes the statement in the program and then checks the condition.

Syntax:

DO

[statement]

LOOP WHILE [condition] END

Example:

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

DO UNTIL loop

The DO UNTIL loop repeats a group of code as long as the given condition is false.

Syntax:

DO UNTIL [condition]

[statement]

LOOP END

Example:

CLS  
count = 0  
DO UNTIL count = 10
  count = count + 1
  PRINT "Count is now " + STR$(count)
LOOP
END

WHILE WEND looping statement

A WHILE...WEND loop statement runs all the statements as long as the condition is True. If the condition becomes False, the loop ends and the program continues with the statement after the WEND keyword.

Syntax:

CLS
WHILE [condition]

[statement]

WEND END

Example:

CLS
n = 20
WHILE n < 25
PRINT n
n = n+1
WEND
END

NESTED FOR…NEXT looping statement

When we use FOR NEXT loop inside another FOR NEXT loop statement, we call the statements the NESTED FOR...NEXT looping statement.

The outer FOR NEXT statement that engulfs the inner second FOR NEXT statement is called the Outer Loop.

And the second FOR NEXT statement that is inside the outer loop is called the Inner Loop.

Syntax:

FOR [outer variable] = starting value TO ending value
    FOR [inner variable] = starting value TO ending value
        [Statements to be executed]
    NEXT [inner variable]
NEXT [outer variable]

Example:

FOR i = 1 TO 3 ' Outer Loop
    FOR j = 1 TO 2 ' Inner Loop
        PRINT "i = "; i; ", j = "; j
    NEXT j
NEXT i

Conclusion:

In conclusion, we can say that looping statements are a fundamental part of learning a programming language. It helps us to reduce code and help the program run effectively.

In QBASIC, there are four main looping statements FOR NEXT, NESTED FOR NEXT, WHILE WEND, and DO LOOP. In this article on QBASIC looping statement, we have understood all four loop statements along with their syntax and examples.

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