I am working on a home work assignment which is:
"Write a program that will allow the user to enter an infix expression terminated by '=' your program will convert to Postfix notation"

enter 3+7-6/2*8+7=
prints 3 7 + 6 2 / 8 * - 7 +

I have written the code below to complete this useing single digits, but I want to allow the user to put in any number and have it do the same
ie 37+47/12 prints 37 47 + 12/

This is not part of the assignment, but I have the next two week to fiddle with it.
Any suggestion? I am lost at the moment.

Thanx in advance!
Lanier

char InOp1='#'; //Holds values to be compared in switch case.
char InOp2='#'; //Holds value for comparison to properly push onto stack.
LinkedStack Cal; //stack used to hold info in postfix format

void In2Post()
	{
		cin>>InOp1;
	
		while(InOp1!='=')
		{
	
			//while loop to push digits on to stack
			while(InOp1!='+'&&InOp1!='-'&&InOp1!='*'&&InOp1!='/'&&InOp1!='('&&InOp1!=')'&&InOp1!='?')
			{
				Cal.Push(InOp1);
				cin>>InOp1;
			}
		
			switch(InOp1) //switch case used to properly format stack
			{
				case '+': cin>>InOp2;
					if(InOp2=='+'||InOp2=='-'||InOp2=='*'||InOp2=='/'||InOp2=='('||InOp2==')')
					{
						cout<<"Incorrect input "<<InOp2<<" cannot follow + sign."<<endl<<"Must be digit.";
						InOp1='?';
						break;
					}
					else
					{
						Cal.Push(InOp2);
						Cal.Push(InOp1);
						cin>>InOp1;
						break;
					}
				case '-': cin>>InOp2;
					if(InOp2=='+'||InOp2=='-'||InOp2=='*'||InOp2=='/'||InOp2=='('||InOp2==')')
					{
						cout<<"Incorrect input "<<InOp2<<" cannot follow - sign."<<endl<<"Must be digit.";
						InOp1='?';
						break;
					}
					else
					{
						Cal.Push(InOp2);
						Cal.Push(InOp1);
						cin>>InOp1;
						break;
					}
				case '/': cin>>InOp2;
					if(InOp2=='+'||InOp2=='-'||InOp2=='*'||InOp2=='/'||InOp2=='('||InOp2==')')
					{
						cout<<"Incorrect input "<<InOp2<<" cannot follow / sign."<<endl<<"Must be digit.";
						InOp1='?';
						break;
					}
					else
					{
						Check=Cal.Top();
						if(Check=='+'||Check=='-')
						{
							Cal.Pop();
							Cal.Push(InOp2);
							Cal.Push(InOp1);
							Cal.Push(Check);
							Check='#';
							cin>>InOp1;
							break;
						}
						else
						{
							Cal.Push(InOp2);
							Cal.Push(InOp1);
							Check='#';
							cin>>InOp1;
						}
					}
				case '*': cin>>InOp2;
					if(InOp2=='+'||InOp2=='-'||InOp2=='*'||InOp2=='/'||InOp2=='('||InOp2==')')
					{
						cout<<"Incorrect input "<<InOp2<<" cannot follow * sign."<<endl<<"Must be digit.";
						InOp1='?';
						break;
					}
					else
					{
						Check=Cal.Top();
						if(Check=='+'||Check=='-')
						{
							Cal.Pop();
							Cal.Push(InOp2);
							Cal.Push(InOp1);
							Cal.Push(Check);
							Check='#';
							cin>>InOp1;
							break;
						}
						else
						{
							Cal.Push(InOp2);
							Cal.Push(InOp1);
							Check='#';
							cin>>InOp1;
						}	
					}
				case '(':case ')': cin>>InOp1;
									break;
			
				default: cout<<endl<<"Input data contains error can not continue."<<endl<<endl;
						system("pause");
						return 0;
				
			}
                }

The first thing I would suggest is you parse the expression from a string (and not user input), and return an expression list (not void, and not in a global).

You can then test with

LinkedStack in2post( std::string expr );

int main ( ) {
  std::string expr = "3+7-6/2*8+7=";
  LinkedStack result = in2post( expr );
}

You can then expand the tests with

LinkedStack in2post( std::string expr );

int main ( ) {
  std::string expr[] = {
      "1=",
      "1+2=",
      "1+2*3",
      "3+7-6/2*8+7=",
  };
  for ( int i = 0 ; i < sizeof expr / sizeof *expr ; i++ ) {
    LinkedStack result = in2post( expr[i] );
  }
}

When you're finally happy, then you can do

std::string myExpr;
getline( cin, myExpr );
LinkedStack result = in2post( myExpr );

As far as algorithms go, look up the "shunting yard algorithm".

I would also suggest better formatting. See this and pay particular attention to the Indentation section. As it is your code is very difficult to follow.

First and formost THANX!! Walt for the link I knew my code was hard to read. Sorry for the bad formatting I will fix that soon.

Also thanx for the idea Sal. I will tweak and report back with the results.

Thanx again

Lanier

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