Stack • Applications

Postfix to Infix Conversion

Converting a computer-friendly Postfix expression back into human-readable Infix notation requires explicitly re-introducing parentheses to guarantee correctness.

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The String Stack

Instead of storing operators (like Infix -> Postfix), our stack will now store fully formed String chunks representing valid sub-expressions.

The Assembly

When an operator is encountered, we pop `val2` then `val1`. We immediately wrap them with the operator and parentheses: `(val1 operator val2)`, then push this string back to the stack.

Final Output

By the time the loop ends, the stack will contain exactly one string. That single string is your fully parenthesized Infix expression.

ab*c+

String Stack

Empty

Code Tracker

:::

1function postfixToInfix(exp) {

2 let stack = [];

3 for (let char of exp) {

4 if (isOperand(char)) {

5 stack.push(char);

6 } else {

7 let val2 = stack.pop();

8 let val1 = stack.pop();

9 stack.push('(' + val1 + char + val2 + ')');

10 }

11 }

12 return stack.pop();

13}

Postfix To Infix

Postfix To Infix

Postfix to Infix Conversion

The String Stack

The Assembly

Final Output

Postfix to Infix Conversion

The String Stack

The Assembly

Final Output