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Last Updated: Mar 27, 2024
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Case Statement in Compiler Design

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Prerita Agarwal
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23 Jul, 2024 @ 01:30 PM

Introduction

Compiler design is the process of designing and implementing a compiler. The compilers convert program code written in different languages into machine-readable code that the computer can execute. Syntax analysis is one of the main steps during this process. We do handle different types of statements in this; one of the types of statements is the case statement in compiler design.

Case Statement in Compiler Design

In this blog, we will discuss the case statement in compiler design. It is used to perform different statements based on the input value of the variable. We will also discuss one example to understand its syntax better.

Case Statement in Compiler Design

The case statement in compiler design is a conditional statement used to execute different blocks of code based on the evaluated value of the input expression. It is available in various programming languages, and the syntax varies depending on the language.

Syntax

Let's discuss the general syntax for a case statement in compiler design.

switch <expression> {
	begin
		first case value: statement_1
		second case value: statement_2
		third case value: statement_3
		fourth case value: statement_4
		.
		.
		(n-1)th case value: statement_(n-1)th
		default: statement_nth
	end
}

In the above syntax of a case statement in compiler design, the "switch" keyword initializes the case statement. An input "expression" is evaluated as the first step. The "case" keyword is used to express different values that the expression can take. The evaluated value is then matched with the following case values. For the case whose value matches the expression's value, its corresponding statement block is executed.
 

"break" keyword is also present at the end of every statement in some languages used to exit the case statement if that block of statements is executed. The program might continue to run for the following cases if the break statement has not occurred.

Translation of the Case Statement

code to evaluate E into t 
		goto test
L1:		code for S1
			goto next
L2:		code for S2
			goto next
				.....
Ln-1:		code for Sn-1
			goto next
Ln:		code for Sn
			goto next
test:		if t = 1 goto L1
			if t = 2 goto L2
					.....
			if t = Vn-1   goto Ln - 1
			goto  Ln
next:

When the "switch" keyword is encountered, the "test" and "next" and a temporary variable "t" are generated. A new label, "Li," is also created and used to store the value "Vi" of the constant "Li."
 

Related Article Switch Statements.

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Case Statements in Different Languages

The syntax and functionality of a case statement in compiler design may vary depending on the programming languages. It's essential to follow the syntax rules for the language so that your code is correct. Let's discuss some examples of case statements in different languages.

C/C++

switch (expression) {
	case value:
		// Block of code
		break;
}


Java

switch (expression) {
	case value:
		// Block of code
		break;
}


Python

In the latest version of Python, Python 3.10, match case statements were introduced. The match statements work similarly to the switch statements.

match expression:
	case 1st_value:
		# Block of code
	case 2nd_value:
		# Block of code
	.
	.
	case _:
		# Default block of code

Example in C++

The following code is a simple example of case statement in compiler design.

Code

#include <iostream>
using namespace std;

int main() {
	char curr_grade = 'C';
	switch (curr_grade) {
		case 'A':
			cout << "Excellent work!" << endl;
			break;
		case 'B':
			cout << "Well done!" << endl;
			break;
		case 'C':
		case 'D':
			cout << "You just passed :)." << endl;
			break;
		case 'F':
			cout << "Better luck next time." << endl;
			break;
		default:
			cout << "Invalid Grade" << endl;
	}
	return 0;
}

Output

You just passed :).

In the above example, we discussed the case statement in compiler design in C++ language. It simply shows, depending on the input value of the "curr_grade" variable different statements can be printed. The "switch" keyword evaluates the value of "curr_grade" and executes the case with a matching value.

If the value is 'A,' the program prints "Excellent work!". If the value is 'B,' it prints "Well done!". If the value is 'C' or 'D,' it prints "You just passed :) .". If the value is 'F,' it prints "Better luck next time.". If the value does not match the specified cases, the program executes the default code block and prints "Invalid Grade.".

Frequently Asked Questions

What is a case statement in compiler design used for?

The case statement in compiler design is used to execute a particular block of code for the respected value of the expression. It is an example of a conditional expression.

What is the use of default block in case statements?

If the expression's value does not match with any mentioned cases, in that case, the block of code in the default block is executed. It is usually used for error handling or as a fallback option.

What if a break statement is removed from a case statement? 

If a break statement is absent in a case statement, the program will continue executing the code blocks for subsequent cases until a break statement is encountered. This can lead to unexpected behavior and is generally considered a coding error.

Conclusion

We hope this article was insightful and you learned something new. In this blog, we discussed the case statement in compiler design, a conditional statement used to execute different codes depending on the input expression's value. We learned about its syntax and also saw its translation. We also discussed its syntaxes in various programming languages which helps programmers work in specific languages.

If you want to learn more about compiler design, do visit

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Topics covered
1.
Introduction
2.
Case Statement in Compiler Design
2.1.
Syntax
2.2.
Translation of the Case Statement
3.
Case Statements in Different Languages
4.
Example in C++
4.1.
Code
4.2.
Output
5.
Frequently Asked Questions
5.1.
What is a case statement in compiler design used for?
5.2.
What is the use of default block in case statements?
5.3.
What if a break statement is removed from a case statement? 
6.
Conclusion