conditional statement in qbasic

  

Conditional or Branching statement

 

A conditional statement transfers the control from one part to another by testing the condition.

 

  

IF…THEN Statement:

IF-THEN statement control flows according to the given condition. IF the condition is true the statement of the IF block is executed. If it is not true, the statement in the IF block is not executed.

 

Single Line IF…. THEN statement

This statement is written in a single line. This statement terminates itself when the entire line will be finished so that it does not require an END IF statement like block IF…THEN…ELSE.

 

Syntax: IF condition THEN statement_for_true

 

Example:

To input any number and displayed whether input number is odd or even.

CLS

INPUT “Enter any no”;n

r=n MOD 2

IF r=0 THEN PRINT “Even no”

IF r=1 THEN PRINT “Odd no”

END

 

IF…THEN...ELSE Statement:

It is a two-way branching statement. If the condition is true the statement in IF block is executed, if it is not true then the statement in the ELSE block is executed.

Syntax: (Single line IF….ELSE)

 

        IF <condition> THEN <statement> ELSE <statement>

 

OR

IF (condition) THEN

Statement

ELSE

Statement

END IF

 

Example:1

WAP to input any number and check whether the input number is odd or even

CLS

INPUT "enter any number="; nu

IF  nu MOD 2 = 0 THEN PRINT "Number is even" ELSE PRINT "Number is Odd"

END

Example 2:

CLS

INPUT "enter any number="; n

r = n MOD 2

IF r = 0 THEN

PRINT "Even no"

ELSE

PRINT "Odd no"

END IF

END

 

IF…ELSEIF...ELSE Statement:

It is a multi-way branching statement. This statement is useful when there are motile conditions we have to check. This statement can be used when there is more than one condition to test. This statement tests the first condition, if the condition is correct then its respective code will be executed, if not correct the previous condition, then it will check the second condition, if it is correct then it execute its respective block, if the second condition is not also correct then the else code will be executed. This block end with END IF" line code.

 

Syntax:

          IF (condition 1) THEN

          [statement block 1]

          ELSEIF (condition 2) THEN

          [statement block 2]

          …

          ELSE

          [statement block n]

          END IF

 

Example:

Program to check whether input number is odd or even

CLS

INPUT "enter any no"; n

r = n MOD 2

IF r = 0 THEN

PRINT "even"

ELSEIF r = 1 THEN

PRINT "odd"

ELSE

PRINT "invalid no"

END IF

END

SELECT CASE Statement:

It is a multi-branching conditional statement that controls the branching to one of the several statements based on the value of an expression.

Syntax:

          SELECT CASE test expression

          CASE expression 1

          [statement block 1]

          CASE expression 2

          [statement block 2]

          CASE expression 3

          [statement block 3]

          …………………….

          CASE ELSE

          [statement block]

          END SELECT

  

Example 1: Program to check whether input number is odd or even

CLS

INPUT "Enter any no"; n

r = n MOD 2

SELECT CASE r

CASE 1

PRINT "odd no"

CASE 0

PRINT "even no"

CASE ELSE

PRINT "invalid no"

END SELECT

END

 

Example 2: To check the grade from the input mark

CLS

INPUT “Enter marks : “ ; m

SELECT CASE m

CASE 90 TO 100

PRINT “A+”

CASE 80 TO 89.9

PRINT “A”

CASE 70 TO 79.9

PRINT “B+”

CASE 60 TO 69.9

PRINT "B"

CASE 50 to 59.9

PRINT "C+"

CASE 40 TO 49.9

PRINT "C"

CASE 35 TO 39.9

PRINT "D"

CASE ELSE

PRINT "NG"

END SELECT

END

 

Note: Always write smaller to bigger value, when give expression  (CASE 90 TO 100) which indicates range.

 

Example: Program to find the area of circle, area or rectangle and area of triangle with the help of menu structure.

CLS

PRINT "c. Area of circle"

PRINT "r. area of rectangle"

PRINT "t. Area of triangle"

INPUT "Enter your choice"; ch$

SELECT CASE ch$

CASE "C", "c"

INPUT "Emter radois"; r

a = 3.14 * r * r

PRINT "Area of circle"; a

CASE "R", "r"

INPUT "Enter length:"; l

INPUT "Enter breadth"; b

ar = l * b

PRINT "Area of rectangle"; ar

CASE "T", "t"

INPUT "Enter base:"; b

INPUT "Enter height:"; h

at = 1 / 2 * b * h

PRINT "Area of triangle:"; at

CASE ELSE

PRINT "invalid choice"

END SELECT

END

 

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