In this lab you are going to write reverse postfix calculator using a stack. Pos

Question

In this lab you are going to write reverse postfix calculator using a stack. Postfik notation and is parenthesis- free as long as operator arities are fixod. In postfix notation the gperators follow their operands; for instance, to add 3 and 4, one would write 34+'rather than "3+4". If there are multiple operations, the operator is given immediately after its second operand; so the expression written 3-4+5" in conventional notation would be written "34-5+ in postfix: first subtract 4 from 3, then add 5 to that. An advantage of postfix is that it eliminates the need for parentheses that are required by infix. While "3 can also be written "3-(4 5)", that means something quite different from '(3-4)*5". In postflx, the former could be written "345", which unambiguously means "3 (45)" which reduces to "3 20-" the latter could be written "34.5 (or 534. ",if you wish to keep similar formatting), which unambiguously means "(3 )5 Postfix Notation Value Standard expression 1+3 10/5 1 3+ 105/ 1016+2.3)1062-3- The program logic read in a string while the string is not "stop" if the string is+ pop the last 2 values from the stack and push back their sum else if the string is pop the last 2 values from the stack and push back their product else if the string is pop the last 2 values from the stack and push back the second else if the string is /, pop the last 2 values from the stack and push back the second - the first / the first else if string is print the top of the stack and pop the stack else (//the string is a number), convert to a double and push it on the stack; read the next string

Explanation / Answer

Code

#include <iostream>
#include <fstream>
#include <stack>
using namespace std;
bool isOperator(char ch)
{
if (ch=='+' || ch=='-' || ch=='*' || ch=='/' || ch == '%')
return true;
else
return false;
}

int performOperation(int op1, int op2, char op)
{
int ans;
switch(op){
case '+':
ans = op2 + op1;
break;
case '-':
ans = op2 - op1;
break;
case '*':
ans = op2 * op1;
break;
case '/':
ans = op2 / op1;
break;
case '%':
   ans = op2 % op1;
   break;
}
return ans;
}
int main()
{
string post;
char buffer[15];
int i,op1, op2, len, j, x, numOfExpressions;
stack<int> s;
size_t bufSize = 256;
while(true)
{
cout << "Type in a postfix expression or stop to stop: ";
getline(cin, post);
if(post.compare("stop") == 0)
   return 0;
//for(int k = 0; k < numOfExpressions; k++)
{
//fgets(post, 250, fin);
//fin.getline ( post, 256, ' ' );
len = post.length(); //strlen(post);
j = 0;
for(i=0; i<len;i++){

if(post[i]>='0' && post[i]<='9'){
buffer[j++] = post[i];
}
else if(post[i]==' '){
if(j>0){
buffer[j] = '';
x = atoi(buffer);
s.push(x);
j = 0;
}
}

else if(isOperator(post[i])){
op1 = s.top();
s.pop();
op2 = s.top();
s.pop();
s.push(performOperation(op1, op2, post[i]));
}
}
printf("%s = %d ", post.c_str(), s.top());
}
}
}

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