// C++ Program infix to postfix expression using stack (array) in data structure
#include<iostream>
#include<string>
#define MAX 20
using namespace std;
char stk[20];
int top=-1;
// Push function here, inserts value in stack and increments stack top by 1
void push(char oper)
{
if(top==MAX-1)
{
cout<<"stackfull!!!!";
}
else
{
top++;
stk[top]=oper;
}
}
// Function to remove an item from stack. It decreases top by 1
char pop()
{
char ch;
if(top==-1)
{
cout<<"stackempty!!!!";
}
else
{
ch=stk[top];
stk[top]='\0';
top--;
return(ch);
}
return 0;
}
int priority ( char alpha )
{
if(alpha == '+' || alpha =='-')
{
return(1);
}
if(alpha == '*' || alpha =='/')
{
return(2);
}
if(alpha == '$')
{
return(3);
}
return 0;
}
string convert(string infix)
{
int i=0;
string postfix = "";
while(infix[i]!='\0')
{
if(infix[i]>='a' && infix[i]<='z'|| infix[i]>='A'&& infix[i]<='Z')
{
postfix.insert(postfix.end(),infix[i]);
i++;
}
else if(infix[i]=='(' || infix[i]=='{' || infix[i]=='[')
{
push(infix[i]);
i++;
}
else if(infix[i]==')' || infix[i]=='}' || infix[i]==']')
{
if(infix[i]==')')
{
while(stk[top]!='(')
{ postfix.insert(postfix.end(),pop());
}
pop();
i++;
}
if(infix[i]==']')
{
while(stk[top]!='[')
{
postfix.insert(postfix.end(),pop());
}
pop();
i++;
}
if(infix[i]=='}')
{
while(stk[top]!='{')
{
postfix.insert(postfix.end(),pop());
}
pop();
i++;
}
}
else
{
if(top==-1)
{
push(infix[i]);
i++;
}
else if( priority(infix[i]) <= priority(stk[top])) {
postfix.insert(postfix.end(),pop());
while(priority(stk[top]) == priority(infix[i])){
postfix.insert(postfix.end(),pop());
if(top < 0) {
break;
}
}
push(infix[i]);
i++;
}
else if(priority(infix[i]) > priority(stk[top])) {
push(infix[i]);
i++;
}
}
}
while(top!=-1)
{
postfix.insert(postfix.end(),pop());
}
cout<<"The converted postfix string is : "<<postfix; //it will print postfix conversion
return postfix;
}
int main()
{
int cont;
string infix, postfix;
cout<<"\nEnter the infix expression : "; //enter the expression
cin>>infix;
postfix = convert(infix);
return 0;
}
Output:-
Enter the infix expression : a=b*2+5
The converted postfix string is : ab*=+25
Kaynak :
[https://prepinsta.com/cpp-program/infix-to-postfix-conversion-using-stack/]
