Me+string+class= clueless

[iM0CKusALL]

Hi. I'm a novice to programming with 2 years of daydreaming through my programming classes and am now stuck with a unresponsive online teacher with horrible assignment instructions. The assignment is due today so I'm not asking how to do it. I've just been screwing around with example problems I've found and manipulated them to suit my purpose. Commented out sections of code are just some of my thinking/monkeying around. Excuse them. The code below has none of my classes included. Its purely trying to work out the basics of the assignments objectives.

My questions:
-How to convert a string to a double? //(strtod? atof?
-How could you take a string that the user enters and identify the numbers in it?
// say the users string was "2*x*x-13*x+4" : how to identify that its '13' and //not '1' and '3'?

-How to identify that the numbers as negative and positive from the string?
-How to offset find to that it continues to find the rest of the 'x' in the string?
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#include <stdio.h>
#include <string.h>
#include <cstdlib>	//need this for exit function
#include <iostream>	//need this for cout
#include <cmath>	
#include <stdlib.h>     /* strtod */
using  namespace std;

int main ()
{
	char str[256];
        cout << "enter numbers and symbols: \n";
        cin >> str;
        char * pch;
        char * pchb;
        const int SIZE =100;
        char keys[] = "1234567890";
 //char keystwo[] = "x*+-";

  //double array[SIZE];
  //for(int count=0; count<=9;count++)//change 9 to biggest degree
  //{
	     pchb = strpbrk (str,keys);
	     while(pchb !=NULL)
	      {
		                   //array[count] = strtod (pchb,NULL);
		                  //char coef[count]= *pchb;//collectthe coefficents
			printf ("%c " , *pchb);
			pchb = strpbrk (pchb+1,keys);
		}
  //}
  // for(int i=0; i<=;i++)//change 9 to biggest degree
  //{
 // printf ("double : %c",array[i]);
   //}
	         printf ("\nSplitting string \"%s\" into tokens:\n",str);
		pch = strtok (str," +*x");
	        while (pch != NULL)
	          {
		                                        //char coeftwo[count] = pch;
		           printf ("%s\n",pch);
		           pch = strtok (NULL, " +*x");
	            }
  
  system("pause");
  return 0;
}

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So far the I've gotten the above code to print out this:(EXAMPLE)

enter numbers and symbols:
2*x*x*x*x-13*x*x*x*x+0*x*x-7
2 1 3 0 7
slitting string "2*x*x*x*x-13*x*x*x*x+0*x*x-7" into tokens:
2
-13
0
7
Press any key to coutinue...

_

_______________________________________________



Bonus Info:
The assignment is called Polynomial Class and after going to my programming teacher in high school we think we figured out what the assignment was asking.

INTERPRETATION OF ASSIGNMENT:
Using dynamic arrays, implement a polynomial class with infix operators +, -, *.

It has the user enter a string a polynomial in the form of having x*x to signify the degree of the polynomial. (EX: x^2 == x*x, x^4==x*x*x*x, etc)

The student is to provide these member functions:
-default constructor,
-copy constructor,
-operator=
-destructor
-parameterized constructor to create an arbitrary polynomial

-operator+
-operator-
-operator*
-assign and inspect function (or functions) for
-coefficients, indexed by exponent
-function to evaluate polynomial as a value of type double
The student is to decide on whether these are to be member, friend, or neither (standalone).

The program should print statements like this...
(EX:
2x^3 -3x + 4 (or, written out as C++ code) 2*x*x*x –3*x + 4
the coefficients for terms as listed:

"degree 3 term has coefficient 2,
degree 2 term has coefficient 0,
degree 1 term has coefficient -3, and
degree 0 term has coefficient 4. " )

[iM0CKusALL]

A previous question that seem to be a simular assignment if not he same is at:
http://www.cplusplus.com/forum/beginner/39735/

It talks about the basics of the class part of the assignment.

I'm mostly concerned with manipulating the string though.

[iM0CKusALL]

(I would like to do...)

--end print statements are already done.

--I thought I would use the "+" and "-" symbols to help separate the different degrees.

-- I can to identify the coefficient by the numbers 0-9 till "*" operator found.

--I thought I would also find biggest degree and set that to equal the array[size] which I would then initialize all elements to zero (taking care of any unspoken/implied zero coefficients. EX: 0*x^3) then corresponding array elements to known coefficient values.

Yes, I know that arrays shouldn't be used here because you cannot determine the exact size it should be. BUT the instructions say dynamic array. (Course it also mentions linked lists and something called STL and how the two could fix this problem but then the instructions goes on to say "will discuss later". Which is laughable because the course is online and we don't really "discuss" anything. He just posts the assignment, we do it, we turn it in, he posts another one, and on the cycle goes.)

But my experience and understanding of sting manipulation is poor. An adequate visual of me coding string is that of a one year old trying to fit a square in the triangle hole.

I don't think I'm looking at this problem correctly. As in merging the class and call member functions part with the string part.

Any advice, observations, explanations, or mad ravings are welcome.