#include <iostream>
#include <stack>
using namespace std;
int prec (char ch){
// Gives precedence to different operators
switch (ch) {
case '^':
return 5;
case '/':
return 4;
case '*':
return 4;
case '+':
return 2;
case '-':
return 1;
default :
return 0;
}
}
bool isOperand(char ch){
// Finds out is a character is an operand or not
if ((ch>='0' && ch<='9') (ch>='a' && ch<='z'))
return true;
else
return false;
}
string postFix (string infix){
string pfix = "";
stack<char> opstack;
for (int i=0; i<infix.length(); i++){
// Scan character by character
if (isOperand(infix[i]))
{
pfix += infix[i];
}
else if (infix[i] ')')
{
// Retrace to last ( closure
while (opstack.top() != '(')
{
pfix += opstack.top();
opstack.pop();
}
// Remove the '(' found by while loop
opstack.pop();
}
If this is a homework assignment, please consider trying to answer it yourself first, otherwise the value of the reinforcement of the lesson offered by the assignment will be lost on you.
To convert infix notation to postfix notation, parse the expression into tokens. As you encounter an operand, push it onto one stack. As you encounter an operator, consider its precedence level and, if it is higher than the current precedence level, push it and the precedence level onto a second stack. Note that the parenthesis is a special operator that overrides precedence level, raising it.
When you encounter an operator with a precedence level equal to or lower than the current precedence level, pop the operand(s) off of the first stack, output them, and the pop the operator off of the second stack (unless it was not pushed in the first place) and output it. As you pop things off of the stacks, consider the current precedence level against the current precedence level, and iterate the pop/output sequence as needed.
people almost exclusively use infix notation to write mathematical expressions, computer languages almost exclusively allow programmers to use infix notation. However, if a compiler allowed infix expressions into the binary code used in the compiled version of a program, the resulting code would be larger than needed and very inefficient. Because of this, compilers convert infix expressions into postfix notation expressions, which have a much simpler set of rules for expression evaluation. Postfix notation gets its name from the fact that operators in a postfix expression follow the operands that they specify an operation on. Here are some examples of equivalent infix and postfix expressions Infix Notation Postfix Notation 2 + 3 2 3 + 2 + 3 * 6 3 6 * 2 + (2 + 3) * 6 2 3 + 6 * A / (B * C) + D * E - A - C A B C * / D E * + A C * - Where as infix notation expressions need a long list or rules for evaluation, postfix expressions need very few.
infix: old Egyptians/Assirs some thousands year before prefix: Jan Łukasiewicz (Polish Notation) postfix: Burks, Warren, and Wright (Reverse Polish Notation)
/**************************//**********cReDo**********//*****mchinmay@live.com***///C PROGRAM TO CONVERT GIVEN VALID INFIX EXPRESSION INTO POSTFIX EXPRESSION USING STACKS.#include#include#include#define MAX 20char stack[MAX];int top=-1;char pop();void push(char item);int prcd(char symbol){switch(symbol){case '+':case '-':return 2;break;case '*':case '/':return 4;break;case '^':case '$':return 6;break;case '(':case ')':case '#':return 1;break;}}int isoperator(char symbol){switch(symbol){case '+':case '-':case '*':case '/':case '^':case '$':case '(':case ')':return 1;break;default:return 0;}}void convertip(char infix[],char postfix[]){int i,symbol,j=0;stack[++top]='#';for(i=0;iprcd(stack[top]))push(symbol);else{while(prcd(symbol)
/**************************//**********cReDo**********//*****mchinmay@live.com***///C PROGRAM TO CONVERT GIVEN VALID INFIX EXPRESSION INTO POSTFIX EXPRESSION USING STACKS.#include#include#include#define MAX 20char stack[MAX];int top=-1;char pop();void push(char item);int prcd(char symbol){switch(symbol){case '+':case '-':return 2;break;case '*':case '/':return 4;break;case '^':case '$':return 6;break;case '(':case ')':case '#':return 1;break;}}int isoperator(char symbol){switch(symbol){case '+':case '-':case '*':case '/':case '^':case '$':case '(':case ')':return 1;break;default:return 0;}}void convertip(char infix[],char postfix[]){int i,symbol,j=0;stack[++top]='#';for(i=0;iprcd(stack[top]))push(symbol);else{while(prcd(symbol)
It's simply a matter of where the operators are placed in relation to their operands: infix: X + Y prefix: + X Y postfix: X Y + All of the above are equivalent. Prefix notation is also known as Polish notation, hence postfix is also known as reverse Polish notation. Given the infix equation A * B + C / D, the order of evaluation is always parenthesis, orders, divide/multiply, add/subtract (PODMAS), thus we must multiply A by B first, then divide C by D, and finally add the two results together. If we wish to perform the addition first, then we must re-write the equation with parenthesis: A * (B + C) / D. With postfix and prefix notation, operator precedence becomes superfluous because we always evaluate these expressions in left-to-right order: Infix A * B + C / D becomes postfix A B * C D / + or prefix / * A + B C D Infix A * (B + C) / D becomes postfix A B C + * D / or prefix + * A B / C D When we eliminate operator precedence with postfix or prefix notation, we greatly simplify the algorithm required to evaluate complex expressions. For example, given the postfix expression A B C + * D /, we simply read the symbols one at a time, placing them on a stack, until we encounter an operator. We then pop the first two elements off the stack, perform the operation, and then pop the result back on the stack. We repeat this process until there are no more symbols left, at which point the stack holds just one value: the result. With prefix notation, we place the operators on the stack instead of the operands. When we read the first operand we simply store it in an accumulator. We continue pushing operators onto the stack until we encounter the second operand, at which point we can pop the first operator off the stack, perform the operation and update the accumulator. We repeat this process until there are no symbols left, at which point the accumulator holds the final result. Note that when presented with an infix expression, a machine has to convert the expression to the equivalent prefix or postfix expression before it can be evaluated. By eliminating this conversion process, computation by machine can be performed with much greater speed.
stack is the basic data structure needed to convert infix notation to postfix
people almost exclusively use infix notation to write mathematical expressions, computer languages almost exclusively allow programmers to use infix notation. However, if a compiler allowed infix expressions into the binary code used in the compiled version of a program, the resulting code would be larger than needed and very inefficient. Because of this, compilers convert infix expressions into postfix notation expressions, which have a much simpler set of rules for expression evaluation. Postfix notation gets its name from the fact that operators in a postfix expression follow the operands that they specify an operation on. Here are some examples of equivalent infix and postfix expressions Infix Notation Postfix Notation 2 + 3 2 3 + 2 + 3 * 6 3 6 * 2 + (2 + 3) * 6 2 3 + 6 * A / (B * C) + D * E - A - C A B C * / D E * + A C * - Where as infix notation expressions need a long list or rules for evaluation, postfix expressions need very few.
infix: old Egyptians/Assirs some thousands year before prefix: Jan Łukasiewicz (Polish Notation) postfix: Burks, Warren, and Wright (Reverse Polish Notation)
You convert an (infix) expression into a postfix expression as part of the process of generating code to evaluate that expression.
(a + b) * c / ((x - y) * z)
Linear data structure is used to convert the logical address to physical address .Stack is used in this and the various conversion such as postfix,prefix and infix notation are come in this
To convert an infix expression to a postfix expression in C programming, you can use the Shunting Yard algorithm. This algorithm allows you to scan the infix expression from left to right, and based on the precedence of operators, convert it to a postfix expression. You can use a stack to hold operators and output queue to store the final postfix expression. By following the algorithm, you can convert the infix expression to postfix successfully.
Without data-structures you cannot even store expressions, let alone convert or evaluate them.
/**************************//**********cReDo**********//*****mchinmay@live.com***///C PROGRAM TO CONVERT GIVEN VALID INFIX EXPRESSION INTO POSTFIX EXPRESSION USING STACKS.#include#include#include#define MAX 20char stack[MAX];int top=-1;char pop();void push(char item);int prcd(char symbol){switch(symbol){case '+':case '-':return 2;break;case '*':case '/':return 4;break;case '^':case '$':return 6;break;case '(':case ')':case '#':return 1;break;}}int isoperator(char symbol){switch(symbol){case '+':case '-':case '*':case '/':case '^':case '$':case '(':case ')':return 1;break;default:return 0;}}void convertip(char infix[],char postfix[]){int i,symbol,j=0;stack[++top]='#';for(i=0;iprcd(stack[top]))push(symbol);else{while(prcd(symbol)
/**************************//**********cReDo**********//*****mchinmay@live.com***///C PROGRAM TO CONVERT GIVEN VALID INFIX EXPRESSION INTO POSTFIX EXPRESSION USING STACKS.#include#include#include#define MAX 20char stack[MAX];int top=-1;char pop();void push(char item);int prcd(char symbol){switch(symbol){case '+':case '-':return 2;break;case '*':case '/':return 4;break;case '^':case '$':return 6;break;case '(':case ')':case '#':return 1;break;}}int isoperator(char symbol){switch(symbol){case '+':case '-':case '*':case '/':case '^':case '$':case '(':case ')':return 1;break;default:return 0;}}void convertip(char infix[],char postfix[]){int i,symbol,j=0;stack[++top]='#';for(i=0;iprcd(stack[top]))push(symbol);else{while(prcd(symbol)
An algorithm can not be written with the following infix expression without knowing what the expression is. Once this information is included a person will be able to know how to write the algorithm.
Yes