dato datuashvili dato datuashvili -4 years ago 84
C++ Question

postfix -expression evaluation

I am trying to implement postfix-expression evaluation, here is my code:

#include<iostream>
#include<string.h>
using namespace std;
template < class T > class Stack {
private:
T * s;
int n;
public:
Stack(int maxn) {
s = new T[maxn];
n = 0;
}
int empth() const {
return n == 0;
}
void push(T item) {
s[n++] = item;
}
int pop() {
return s[--n];
}
};

int main()
{
string a = "598+46**7+*";
int n = a.length();
Stack < int >save(n);
for (int i = 0; i < n; i++) {
if (a[i] == "+")
save.push(save.pop() + save.pop());
if (a[i] == "*")
save.push(save.pop() * save.pop());
if ((a[i] >= '0') && (a[i] <= '9'))
save.push(0);
while ((a[i] >= '0') && (a[i] <= '9'))
save.push(10 * save.pop() + (a[i++] - '0'));
}

cout << save.pop() << endl;

return 0;
}


But I get a compile error (I am implementing it in linux (ubuntu 11.10)):

postfix.cpp:35:13: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
postfix.cpp:37:10: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]


How do I fix this?

Answer Source
for(int  i=0;i<n;i++){
  if(a[i]=="+")
    save.push(save.pop()+save.pop());
  if(a[i]=="*")

You need to use single quotes when you are comparing characters

for(int  i=0;i<n;i++){
  if(a[i]=='+')
    save.push(save.pop()+save.pop());
  if(a[i]=='*')
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