How to Handle Parentheses in Infix to Postfix Expression Conversion?

Handling Parenthesis in Infix to Postfix Expression Conversion

Converting infix expressions to postfix expressions is a common task in compiler design. Handling parenthesis correctly is crucial to ensure accurate conversion.

Your question involves handling parenthesis in your Java method, toPostFix. To resolve this, follow these steps:

When encountering an open parenthesis (:

// opening (
if (in_fix.peek().type == 4) {   
    post_fix.push(in_fix.pop());
}

When encountering a closed parenthesis ):

//closing )
if(in_fix.peek().type == 5){
    while(!(post_fix.isEmpty() || post_fix.peek().type == 4)){
         postfixstr.append(post_fix.pop());
    }
    if (post_fix.isEmpty())
        ; // ERROR - unmatched )
    else
        post_fix.pop(); // pop the (
    in_fix.pop(); // pop the )
} 

This process ensures that:

• Left parenthesis ( is pushed onto the post_fix stack.
• When a right parenthesis ) is encountered, operators and non-parenthesis tokens are popped from post_fix and appended to the postfixstr until a left parenthesis ( is encountered on post_fix.
• The left parenthesis is popped, and the right parenthesis is popped from in_fix to match the parenthesis pair.

By implementing these steps, your toPostFix method will correctly handle multiple layers of parenthesis in infix expressions.

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