The Postfix notation is used to represent algebraic expressions. The expressions written in postfix form are evaluated faster compared to infix notation as parenthesis are not required in postfix. We have discussed. In this post, evaluation of postfix expressions is discussed.Following is algorithm for evaluation postfix expressions.1) Create a stack to store operands (or values).2) Scan the given expression and do following for every scanned element.a) If the element is a number, push it into the stack.b) If the element is a operator, pop operands for the operator from stack. Evaluate the operator and push the result back to the stack3) When the expression is ended, the number in the stack is the final answerExample:Let the given expression be “2 3 1. + 9 -“.

• Infix To Postfix Expression
• Prefix Expression

We scan all elements one by one.1) Scan ‘2’, it’s a number, so push it to stack. Stack contains ‘2’2) Scan ‘3’, again a number, push it to stack, stack now contains ‘2 3’ (from bottom to top)3) Scan ‘1’, again a number, push it to stack, stack now contains ‘2 3 1’4) Scan ‘.’, it’s an operator, pop two operands from stack, apply the. operator on operands, we get 3.1 which results in 3. We push the result ‘3’ to stack. Stack now becomes ‘2 3’.5) Scan ‘+’, it’s an operator, pop two operands from stack, apply the + operator on operands, we get 3 + 2 which results in 5.

We are assuming that both operators and operands in input will be single character. InfixToPostfix.cpp. Infix to Postfix conversion in C using stack. We are assuming that both operators and operands in input will be single character. // Function to evaluate Postfix expression and return output string InfixToPostfix(string str). Oct 11, 2011  C Program for Evaluation of Postfix Expression In this program we evaluate the Postfix Expression, using the stack. For example, 456.+7- is the postfix expression, from left one by one it is inserted into the stack, and after evaluation the answer is 27. Read more about C Programming.

We push the result ‘5’ to stack. Stack now becomes ‘5’.6) Scan ‘9’, it’s a number, we push it to the stack. Stack now becomes ‘5 9’.7) Scan ‘-‘, it’s an operator, pop two operands from stack, apply the – operator on operands, we get 5 – 9 which results in -4. We push the result ‘-4’ to stack. Stack now becomes ‘-4’.8) There are no more elements to scan, we return the top element from stack (which is the only element left in stack). FilternoneOutput: postfix evaluation: -4Time complexity of evaluation algorithm is O(n) where n is number of characters in input expression.There are following limitations of above implementation.1) It supports only 4 binary operators ‘+’, ‘.’, ‘-‘ and ‘/’. It can be extended for more operators by adding more switch cases.2) The allowed operands are only single digit operands.

The program can be extended for multiple digits by adding a separator like space between all elements (operators and operands) of given expression.Below given is the extended program which allows operands having multiple digits.

Infix To Postfix Expression

Learn how to evaluate Postfix expression using Stack in C Programming Language. This C code for postfix evaluation takes in a postfix expression from the user and then evaluates it.What is Postfix Expression?In a postfix operation, he operators are placed after the operands. On scanning the expression from left to right, first the operands are recieved and then the operators. Steps To Evaluate a Postfix Expression. Scan the characters of the postfix string from left to right one by one.

Prefix Expression

If the character is an operand then push it on the stack. If the character is an operator then pop two elements from the stack and apply the operator to these two characters. Now, push the result on the stack. After all the characters have been scanned, pop the remaining element of the stack and that is the value of the arithmetic postfix expression.ExampleInfix Expression: (3 + 4). (2 / 2)Postfix Expression: 34+22/.