#include<iostream>
#include<string>
#include<cstdlib>
using namespace std;
char ifx[50],pfx[50],stk[50];
int top=-1,n;
void push(char ch)
{
    if(top!=n)
    {
        ch=stk[top];
        top++;
        cout<<"\nElement added was "<<ch;
    }
    else
        cout<<"\nThe stack is full.";    
}
void pop()
{
    char rmv;
    if(top!=-1)
    {
        rmv=stk[top];
        top--;
        cout<<"\nElement removed was "<<rmv;
    }
    else
        cout<<"\nThe stack is empty.";
}
char topele()
{
    char t;
    if(top!=-1)
        t=stk[top];
    else
    {
        t='#';
        cout<<"\nThere are no elements in the stack.The stack is: "<<t;
    }
    return t;
}
int chkpres()
{
    char ch;
    switch(ch)
    {
        case '^': return 5;
            break;
        case '*': return 4;
            break;
        case '/': return 3;
            break;
        case '+': return 2;
            break;
        case '-': return 1;
            break;
        default: exit(1);
            break;
    }
}
int main()
{
    char pre,pres,ele,elem,chk,popp,topp;
    cout<<"\nEnter how many elements you want to enter in the infix expression: ";
    cin>>n;
    for(int j=0;j<n;++j)
    {
        cout<<"\nEnter the characters of the infix expression one by one: ";
        cin>>ifx[j];
    }
    topp=topele();
    for(int i=0;ifx[i]='\0';++i)
    {
        if(ifx[i]=='(')
        {
            break;
        }
        if(ifx[i]=='^'||ifx[i]=='*'||ifx[i]=='/'||ifx=='+'||ifx[i]=='-')
        {
            if(topp=='^'||topp=='*'||topp=='/'||topp=='+'||topp=='-')
            {
                pre=ifx[i];
                pres=topp;
                chk=chkpres();
                if(pre>pres)
                {
                    topp=pre;
                    top++;
                }
                else if(pres>=pre)
                    pfx[i]=pres;
            }    
        }
        else if(ifx[i]=')')
        {
            while(topp!='#')
            {
                popp=topp;
                pfx[i]=popp;
            }
        } 
    }
    cout<<"\nThe postfix expression is: ";
    for(int i=0;pfx[i]!='\0';++i)
    {
        cout<<pfx[i];
    }
return 0;
}

lab1.cpp:80: error: ISO C++ forbids comparison between pointer and integer