Need to write a program that evaluates a postfix expression which is input by the user and then displays the answer.

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naveen selvan
naveen selvan 2017-2-2
评论： Walter Roberson 2017-2-7
For example, if the user inputs 493*+ then the program should evaluate this postfix expression and display the answer. The user input can vary and the total number of characters may also vary. So, this should also be taken into consideration while writing the program. Thanks!

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回答（1 个）

Bjorn Gustavsson
Bjorn Gustavsson 2017-2-2
If you want us to do your assignments you might have a better chance if you explicitly ask us to. What have you done so far?
Small tip: if current character (token rather!) is a number put it on a stack, if it is an operator take contents of stack and perform operation on those.
HTH
  2 个评论
naveen selvan
naveen selvan 2017-2-7
Thanks for the reply. But, I am unable to convert a postfix expression into individual characters. For example, if the user inputs 123*+ as the postfix expression, I am currently storing it as a string. But, then I am unable to read the string by one character at a time. So, I am stuck right there. If I could read the individual characters, I could solve the rest as the logic is quite simple. Pls help!
Walter Roberson
Walter Roberson 2017-2-7
current_position = 5
current_character = input_string(current_position)
if current_character == '0'
... do something appropriate
elseif current_character == '2'
.... do something appropriate
elseif current_character == '{'
... do something appropriate
elseif current_character == '⁞'
... do something appropriate
end

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