C++ || Stack Based Postfix Evaluation (Single Digit) This page consists of another homework assignment which was presented in a C++ Data Structures course. While the previously discussed program dealt with converting Infix expressions to Postfix, this program will demonstrate exactly how to evaluate them.

NOTE: Want to convert & evaluate multi digit, decimal, and negative numbers? Click here!

REQUIRED KNOWLEDGE FOR THIS PROGRAM

What Is Postfix?
How To Convert Infix To Postfix Equations
Stack Data Structure
Cin.getline
How To Evaluate Postfix Expressions
The Order Of Operations
#include "ClassStackType.h"

The title of this page is called – “Stack Based Postfix Evaluation (Single Digit).” Why “single digit?” The program demonstrated on this page has the ability to evaluate a postfix equation, but it only has the ability to evaluate single digit values. What do I mean by that? Consider the infix equation: 5+2. When that expression is converted to postfix, it will come out to be: 52+, and the answer will be 7 (5+2=7). But what if we have an equation like 12+2? When that expression is converted to postfix, it will come out to be: 122+. The postfix conversion is correct, but when you try to evaluate the expression, we do not know if the math operation should be 12+2 or 1+22, it can be read either way.

Question: So why is this program being displayed if it only works for single digits?
Answer: Because it demonstrates the process of evaluating postfix equations very well.

Want to convert & evaluate multi digit, decimal, and negative numbers? Click here!

Before we get into things, here is a helpful algorithm for evaluating a postfix expression in pseudo code:

Once you understand the process of converting from infix to postfix, adding the ability to evaluate multiple digits within this program should be doable.

======= POSTFIX EVALUATION =======

This program uses a custom template.h class. To obtain the code for that class, click here.

QUICK NOTES:
The highlighted lines are sections of interest to look out for.

Want to convert & evaluate multi digit, decimal, and negative numbers? Click here!

The code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

Once compiled, you should get this as your output
(Note: the code was compile three separate times to display different output)

====== RUN 1 ======

==== Postfix Evaluation ====

Math Operators:
- || Subtraction
* || Multiplication
/ || Division
% || Modulus
^ || Power
\$ || Square Root

Sample Postfix Equation: 45^14*232+\$2-/12%24*/*

Please enter a postfix expression: 1 2 + 5 6 + /
The postfix expression = 1 2 + 5 6 + /

Calculations:
1+2 = 3
5+6 = 11
3/11 = 0.272727

====== RUN 2 ======

==== Postfix Evaluation ====

Math Operators:
- || Subtraction
* || Multiplication
/ || Division
% || Modulus
^ || Power
\$ || Square Root

Sample Postfix Equation: 45^14*232+\$2-/12%24*/*

Please enter a postfix expression: 35*76^+
The postfix expression = 35*76^+

Calculations:
3*5 = 15
7^6 = 117649
15+117649 = 117664

====== RUN 3 ======

==== Postfix Evaluation ====

Math Operators:
- || Subtraction
* || Multiplication
/ || Division
% || Modulus
^ || Power
\$ || Square Root

Sample Postfix Equation: 45^14*232+\$2-/12%24*/*

Please enter a postfix expression: 45^4*32+\$2-/12%24*/*
The postfix expression = 45^4*32+\$2-/12%24*/*

Calculations:
4^5 = 1024
1024*4 = 4096
3+2 = 5
√5 = 2.23607
2.23607-2 = 0.236068
4096/0.236068 = 17350.9
1%2 = 1
2*4 = 8
1/8 = 0.125
17350.9*0.125 = 2168.87