//Convert an infix expression to postfix expression...

#include<iostream>
#include<cstring>
#include<cstdlib>
using namespace std;
char ifx[50],pfx[50],stk[50];
int top=-1,n;
void push(char ch)
{
    if(top!=n-1)
    {
        top++;
        stk[top]=ch;
    }
    else
        cout<<"\nThe stack is full.";    
}
char pop()
{
    char rmv;
    if(top!=-1)
    {
        rmv=stk[top];
        top--;
        return rmv;
    }
    else
        return '#';
}
char topele()
{
    char ch;
    if(top==-1)
    {
        ch='#';
        return ch;
    }   
    else
        ch=stk[top];
}
int chkpres(char ch)
{
    ch=topele();
    switch(ch)
    {
        case '^':return 7;
            break;
        case '/':return 6;
            break;
        case '*':return 5;
            break;
        case '+':return 4;
            break;
        case '-':return 3;
            break;
        default:return 0;
            break; 
     } 
}                 
/*int braces(char *s)
{
    int lftbr,rgtbr=0;
    for(int i=0;s[i];++i)
    {
        if(s[i]=='(')
            lftbr++;
        else
            rgtbr++;
    }
    if(lftbr==rgtbr)
        return 0;
    else if(lftbr<rgtbr)
        return 1;
    else return -1;
}*/
int main()
{
    char ele,elem,chk,popp,topp;
    int pre,pres;
    cout<<"\nEnter how many elements you want to enter in the infix expression: ";
    cin>>n;
    cout<<"\nEnter the infix expression: ";
    for(int i=0;i<n;++i)
        cin>>ifx[i]; 
    topp=topele();
    strcpy(pfx," ");
    for(int i=0,j=0;ifx[i]!='\0',pfx[j]!='\0';++i,++j)
    {
        ele=ifx[i];
        if(ele!='^' && ele!='*' && ele!='/' && ele!='+' && ele!='-')
            pfx[j++]=ifx[i];
        else if(ele=='^'||ele=='*'||ele=='/'||ele=='+'||ele=='-')
        {
            if(topp=='^'||topp=='*'||topp=='/'||topp=='+'||topp=='-')
            {
                pre=chkpres(ele);
                pres=chkpres(topp);
                if(pre>pres)
                {
                    push(pre);
                    top++;
                }
                else if(pre<=pres)
                    pfx[j++]=pres;
            }    
            else
            {
                push(ele);
                topp=ele;
            }
        }
        else if(ele=='(')
        {
            i++;
        }
        else if(ele==')')
        {
            while(topp!='#')
            {
                popp=topp;
                pfx[i]=popp;
            }
        }
        cout<<"---------------"<<pfx[j++];
    }
    cout<<"\nThe postfix expression is: ";
    for(int i=0;pfx[i]!='\0';++i)
    {
        cout<<pfx[i];
    }
    cout<<endl;
return 0;
}