G4G0-2/Data Structures/GPT Answers to Past Paper/Question 6.md

Evaluate the postfix expression 6 2 3 + -.

Postfix Evaluation Rules

1. Operands are pushed onto a stack.
2. Operators pop the required number of operands from the stack, perform the operation, and push the result back onto the stack.
3. Continue until the expression is fully evaluated, and the final value is the only element on the stack.

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Step-by-Step Evaluation

Expression: 6 2 3 + -

1. Read 6:

   • Push 6 onto the stack.
   • Stack: [6]

2. Read 2:

   • Push 2 onto the stack.
   • Stack: [6, 2]

3. Read 3:

   • Push 3 onto the stack.
   • Stack: [6, 2, 3]

4. Read +:

   • Pop the top two operands (3 and 2).
   • Perform 2 + 3 = 5.
   • Push the result (5) onto the stack.
   • Stack: [6, 5]

5. Read -:

   • Pop the top two operands (5 and 6).
   • Perform 6 - 5 = 1.
   • Push the result (1) onto the stack.
   • Stack: [1]

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Final Result:

The result of the postfix expression 6 2 3 + - is 1.