Conditional statements in COBOL allow you to control the flow of execution based on certain conditions. These statements are essential for making decisions within your program. In this section, we will cover the following topics:
- IF Statement
- EVALUATE Statement
- Nested Conditional Statements
- Practical Examples
- Exercises
- IF Statement
The IF statement is used to execute a block of code only if a specified condition is true. The basic syntax is as follows:
Example:
Explanation:
IF AGE > 18: Checks if the value ofAGEis greater than 18.THEN: If the condition is true, the statement followingTHENis executed.ELSE: If the condition is false, the statement followingELSEis executed.END-IF: Marks the end of theIFstatement.
- EVALUATE Statement
The EVALUATE statement is similar to the SWITCH statement in other programming languages. It allows you to evaluate multiple conditions and execute corresponding blocks of code.
Syntax:
EVALUATE TRUE
WHEN condition-1
statement-1
WHEN condition-2
statement-2
WHEN OTHER
statement-3
END-EVALUATE.Example:
EVALUATE TRUE
WHEN AGE < 13
DISPLAY 'Child'
WHEN AGE >= 13 AND AGE < 20
DISPLAY 'Teenager'
WHEN AGE >= 20 AND AGE < 60
DISPLAY 'Adult'
WHEN OTHER
DISPLAY 'Senior'
END-EVALUATE.Explanation:
EVALUATE TRUE: Starts the evaluation.WHEN condition: Specifies a condition to be evaluated.WHEN OTHER: Specifies the default case if none of the conditions are met.END-EVALUATE: Marks the end of theEVALUATEstatement.
- Nested Conditional Statements
You can nest IF statements within other IF statements or within EVALUATE statements to handle more complex conditions.
Example:
IF AGE > 18
THEN
IF AGE < 60
THEN
DISPLAY 'You are an adult.'
ELSE
DISPLAY 'You are a senior.'
END-IF
ELSE
DISPLAY 'You are a minor.'
END-IF.Explanation:
- The outer
IFchecks ifAGEis greater than 18. - The nested
IFchecks ifAGEis less than 60. - Depending on the conditions, the appropriate message is displayed.
- Practical Examples
Example 1: Simple IF Statement
Example 2: EVALUATE Statement
EVALUATE TRUE
WHEN GRADE >= 90
DISPLAY 'A'
WHEN GRADE >= 80
DISPLAY 'B'
WHEN GRADE >= 70
DISPLAY 'C'
WHEN GRADE >= 60
DISPLAY 'D'
WHEN OTHER
DISPLAY 'F'
END-EVALUATE.
- Exercises
Exercise 1: Basic IF Statement
Write a COBOL program that checks if a number is positive, negative, or zero and displays the appropriate message.
Solution:
IDENTIFICATION DIVISION.
PROGRAM-ID. CheckNumber.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 NUMBER PIC S9(4).
PROCEDURE DIVISION.
DISPLAY 'Enter a number:'
ACCEPT NUMBER
IF NUMBER > 0
THEN
DISPLAY 'The number is positive.'
ELSE
IF NUMBER < 0
THEN
DISPLAY 'The number is negative.'
ELSE
DISPLAY 'The number is zero.'
END-IF
END-IF.
STOP RUN.Exercise 2: EVALUATE Statement
Write a COBOL program that categorizes a person's age into different life stages: Child, Teenager, Adult, and Senior.
Solution:
IDENTIFICATION DIVISION.
PROGRAM-ID. AgeCategory.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 AGE PIC 99.
PROCEDURE DIVISION.
DISPLAY 'Enter your age:'
ACCEPT AGE
EVALUATE TRUE
WHEN AGE < 13
DISPLAY 'Child'
WHEN AGE >= 13 AND AGE < 20
DISPLAY 'Teenager'
WHEN AGE >= 20 AND AGE < 60
DISPLAY 'Adult'
WHEN OTHER
DISPLAY 'Senior'
END-EVALUATE.
STOP RUN.Conclusion
In this section, we covered the basics of conditional statements in COBOL, including the IF and EVALUATE statements. We also explored nested conditional statements and provided practical examples and exercises to reinforce the concepts. Understanding these control structures is crucial for making decisions in your COBOL programs. In the next section, we will delve into looping constructs, which allow you to execute a block of code multiple times based on certain conditions.