C++ infix to postfix - c++

Question

I get the following error when I compile:
convert.cpp: In function 'std::string convert()':
convert.cpp:62: error: expected primary-expression before 'else'
convert.cpp:62: error: expected `;' before 'else'
convert.cpp:108: error: expected `}' at end of input
convert.cpp:108: error: expected `}' at end of input
convert.cpp:108: error: expected `}' at end of input
convert.cpp:108: error: expected `}' at end of input
convert.cpp:108: error: expected `}' at end of input
Code:
#include<iostream>
#include<stack>
#include<string>
using namespace std;
string infix; // infix expression string
string operand;
string operate;
stack <string> mystack; // this stack is used to push the operator
string postfix; // postfix string where the operand is appended
//....................................................................
// this function read the infix expression from user
string input()
{
cout<<" Enter the damn infix expression: "<<endl;
getline(cin, infix);
return infix;
}
//......................................................................
// this function checks for operator precedence in the stack
int precedence(string e)
{
int f;
if(e == "*" || e== "/" || e =="%")
f = 2;
else
{
if(e == "+" || e == "-")
f = 1;
}
if(e=="."){
f=0;
}
return f;
}
//....................................................................
// This function converts infix to postfix
string convert()
{
for(int i=0; i<infix.length(); i++)
{
switch(infix[i]){
// operate case start
case '+': case'-': case'*': case'/': case'^': case '(': case ')': case'.':
operate=infix[i];
{
if(mystack.empty() || precedence(operate)>= precedence(mystack.top()))
{
mystack.push(operate);
else
{
while(precedence(operate)<= precedence(mystack.top()))
{
postfix.append(mystack.top());
mystack.pop();
}
mystack.push(operate);
}
}
}//operate case closed
default: //when operand string char is parsed
{
operand=infix[i];
postfix.append(operand);
break;
} // default case closed
}//switch closed
}
while(!mystack.empty())
{
postfix.append(mystack.top())
mystack.pop();
}
return postfix;
cout<<postfix;
}
//...................................................................
int main()
{
input();
convert();
cout<<"postfix is "<<postfix<<endl;
}

Answer 1

It appears that your code is just missing some closing braces. That's all.
For example, look at this:
operate=infix[i];
{
if(mystack.empty() || precedence(operate)>= precedence(mystack.top()))
{
mystack.push(operate);
else
{
while(precedence(operate)<= precedence(mystack.top()))
Where is the closing } before the else statement. Just go through your code and fix these silly mistakes.
It would be a lot easier to rid yourself of these things if you made your spacing and indentation a little neater.

Answer 2

The "expected primary expression before else" diagnostic is the compiler-author's way of reporting you rudely foisted on him an "else" without either a preceding "if" or (what amounts to the same thing) "else if". Alexander Rafferty correctly points out that this is because the code has ...
if (condition) {
// ...
else { }
... when perhaps what you meant was ...
if (condition) {
// ...
}
else {
}
... though maybe you deleted a whole bunch of stuff by accident, and were lucky enough that the deletion resulted in unparseable code, so you will realize that something is wrong.

Answer 3

Look at these lines:
if(mystack.empty() || precedence(operate)>= precedence(mystack.top()))
{
mystack.push(operate);
else