Infix To Postfix Error

[GaryWalker96]

For some reason, I'm getting an error message saying: "Debug assertion failed: Deque iterator not dereferencable. I've read that this error means that I'm popping something off an empty stack, but I don't know why this error is occurring.

This error is being triggered by lines 41-50

stack <string> InfixToPostfix(char * expr)
{
// YOUR CODE STARTS HERE!	
char* token;


stack<string> s;
string postfix;
stack<string> p;
// use stack s to manipulate the infix to postfix
s.push("(");
token = strtok (expr," "); // get the first token
while(!s.empty())
{

if(token=="(")
{
s.push(token);
}

else if(token==")")
{
string c=s.top();
s.pop();
while(c != "(")
{
postfix += c + " ";
c = s.top();
s.pop();
}
}

else if(isNumber(token))
{
postfix+=token;
}

else if(isOperator(token))
{

while(precedence(s.top())>=precedence(token) && !s.empty())
{
string c = s.top();
s.pop();
postfix += c;
postfix += " ";

}
s.push(token);
}



token = strtok(NULL, " "); // use blanks as delimiter
if (token == NULL) // no more tokens, exit the loop
break;





}





p.push(postfix);
return p;
}

[kbw]

It's hard to read your code as there is no indentation. Also, it would be helpful if you posted the code that called that function.

Additionally, you haven't posted precedence() either.