#include <iostream>
#include <string.h>
using namespace std;
#define MAX 100
int st[MAX];
char postfix[MAX],infix[MAX],temp[MAX];
int top=-1;
void push(int a);
int pop();
void infixtopostfix(char temp[],char postfix[]);
void reverse(char str[]);
int getpriority(char);
int main()
{
cout<<"\n\tEnter a infix expression :";
cin>>infix;
infixtopostfix(infix,postfix);
cout<<"\n\tThe postfix expression is : ";
cout<<postfix;
reverse(infix);
infixtopostfix(temp,postfix);
reverse(postfix);
cout<<"\n\tThe prefix expression is : ";
cout<<(temp);
return 0;
}
void reverse(char str[])
{
int i=0,j=0;
int len;
len=strlen(str);
j=len-1;
while(j>=0)
{
if(str[j]=='(')
temp[i]=')';
else if(str[j]==')')
temp[i]='(';
else
temp[i]=str[j];
j--;
i++;
}
temp[i]='\0';
}
void infixtopostfix(char temp[],char postfix[])
{
int i=0,j=0;
char tempo;
while(temp[i]!='\0')
{
if(temp[i]=='(')
{
push(temp[i]);
}
else if(infix[i]==')')
{
while(top!=-1 && st[top]!='(')
{
postfix[j]=pop();
j++;
}
if(top==-1)
{
cout<<"\n\tInvalid Expression";
}
tempo=pop();
i++;
}
else if(isdigit(temp[i]) || isalpha(temp[i]))
{
postfix[j]=temp[i];
j++;
i++;
}
else if(temp[i]=='*' || temp[i]=='/' || temp[i]=='%' || temp[i]=='+' || temp[i]=='-' )
{
while(top!=-1 && st[top]!='(' && getpriority(st[top])>getpriority(temp[i]))
{
postfix[j]=pop();
j++;
}
push(temp[i]);
i++;
}
else
{
cout<<"\n\tInvalid expression";
}
}
while(top!=-1 && st[top]!='(')
{
postfix[j]=pop();
j++;
}
postfix[j]='\0';
}
int getpriority(char op)
{
if(op=='+' || op=='-')
return 0;
else
return 1;
}
void push(int a)
{
if(top==MAX-1)
cout<<"\n\tStack Overflow";
else
{
top++;
st[top]=a;
}
}
int pop()
{
int val;
if(top==-1)
cout<<"\n\tStack Underflow";
else
{
val=st[top];
top--;
}
return val;
}