Polynomial Calculator - c++

Question

I'm doing a polynomial calculator and i'll need some help as i'll progress with the code.
For now I made only the polinom class which i represented it as a linked list with terms and some functions(only read and print the polynomial functions for now).
Here's the main program which for now only read a polynomial and prints it:
#include "polinom.h"
int main()
{
polinom P1;
bool varStatus = false;
char var = '\0', readStatus = '\0';
cout << "P1 = ";
P1.read(readStatus, var, varStatus); // i don't need readStatus yet as i haven't implemented the reset and quit functions
cout << "\n\nP = ";
P1.print(var);
getch();
return 0;
}
And the header file polinom.h:
#ifndef _polinom_h
#define _polinom_h
#include <iostream>
#include <list>
#include <cstdlib>
#include <cctype>
#include <cstdio>
#include <conio.h>
using namespace std;
class polinom
{
class term
{
public:
int coef;
int pow;
term()
{
coef = 1;
pow = 0;
}
};
list<term> poly;
list<term>::iterator i;
public:
bool printable(char c)
{
return (
((int(c) > 42 && int(c) < 123) || isspace(c)) && int(c) != 44 && int(c) != 46 && int(c) != 47 &&
int(c) != 58 && int(c) != 59 &&
int(c) != 60 && int(c) != 61 && int(c) != 62 && int(c) != 63 && int(c) != 64 && int(c) != 65 &&
int(c) != 91 && int(c) != 92 && int(c) != 93 && int(c) != 95 && int(c) != 96
);
}
void read(char &readStatus, char &var, bool &varStatus)
{
term t; // term variable to push it into the list of terms
char c, lc, sign; // c = current char, lc = lastchar and sign the '+' or '-' sign before a coefficient
int coef, pow; //variables to pass the coef and power to term t
bool coefRead = false, powRead = false; //reading status of coef and power
while (c != '\r') { //we read characters until carriage return
c = getch(); // get the new imputed char
if (tolower(c) == 'r' || tolower(c) == 'q') { //if the user inputed r or q we reset the input or quit the program
readStatus = c; //pass current char value to readStatus so the program will know what to do next
return; //aborting the reading process
}
else
{
if (printable(c)) cout << c; //print on screen only the correct characters
if (!coefRead && !powRead) //we set term coef to the inputed value
{
if (isdigit(c)) {
if (isdigit(lc)) coef = coef * 10 + int(c); //if the last char was also a digit we multiply the last value of coef by 10 and add current char
else {
if (sign == '-') coef = -(int(c));//if the current coef has '-' before we set coef to it's negative value
else coef = int(c); //this means a new term's coef is read
}
if (!isdigit(c) && isdigit(lc)) coefRead = true; //if the last char was a digit and we reached the var name we stop reading the coefficient
}
else if (coefRead && !powRead) //after coefficient is read we get the term's varname and power
{
if (isdigit(c)) { // just like in the case with coefficient we read the power until the current char is not a digit
if (isdigit(lc)) pow = pow * 10 + int(c);
else pow = int(c);
}
else if (isalpha(c) && isdigit(lc) && !varStatus) { //if the last char was a digit and the current not we reached the var name
var = c; //also even though the variable is inputed more than once we save it only once
varStatus = true; //we mark the var name as read
}
else {
if (isdigit(lc)) powRead = true;
}
}
else {
if (c == '+' || c == '-') { // if a sign was inputed it means a new term is coming and we push the current term to the list and reset
t.coef = coef; // coefRead and powRead so we can read another term
t.pow = pow;
poly.push_back(t);
sign = c;
coefRead = false;
powRead = false;
}
}
lc = c; // we save the last character
}
}
}
void print(char var)
{
for ( i=poly.begin() ; i != poly.end(); i++ ) { //going through the entire list to retrieve the terms and print them
if (i == poly.end() - 1) { // if we reached the last term
if (*(i->pow == 0) //if the last term's power is 0 we print only it's coefficient
cout << *(i->coef);
else
cout << *(i->coef) << var << "^" << *(i->pow); //otherwise we print both
}
else {
if (*(i->coef > 0) //if the coef value is positive
cout << *(i->coef) << var << "^" << *(i->pow) << " + "; //we also add the '+' sign
else
cout << *(i->coef) << var << "^" << *(i->pow) << " - "; // otherwise we add '-' sign
}
}
}
};
#endif
EDIT
All compile errors fixed now thanks to JonH, but the read function is not working as the input characters aren't correctly inserted into the list. I know it may be trivial for you guys, but it would be great if you help me out.
Thanks!

Answer 1

I found MANY missing curly braces and closing parens all throughout your code. After having spent several minutes fixing at least 10 of these, I thought you would be better served if I helped you to learn to fish, rather than giving you fish for tonight's dinner.
Your code is written like a stream of consciousness. As you are building your code your mind jumps around, thinking of other things you need to build and new requirements introduced by whatever you just wrote. When you think of these things, you go write them and come back to where you were. Before you know it, you have written hundreds of lines of code by jumping around, writing bits here and there. The problem with this is that you can't possibly keep juggling sections of code like this without missing little syntax bits along the way.
You should take a more iterative approach to writing code. How exactly you do this will come with experience, but here's some guidance:
Start by stubbing out a class declaration with a few (preferably 1) core methods and member variables.
Compile. You'll get linker errors and the like, but you shouldn't get any syntax errors like missing parens or semicolons. Fix any you do find before moving on.
Implement the methods/functions you just stubbed. Compile & fix non-linker errors.
As you think of minor or dependant requirements that came up during the above steps, write comments in your code, like // TODO: Implement bool DoTheThing(int); But don't implement them yet.
Loop back to step 1, keeping the scope of what you're working on as limited and fundamental as possible. Never move beyond a compilation step without a clean compile.
Repeat until you have implemented everything. You might compile 50 times or more during this process.

Answer 2

Your fundamental problem is that you wrote a bunch of code down without testing it piece by piece, without thinking about it. When you write as a beginner, you should try adding one little bit at a time and making sure it compiles. Even as an advanced programmer, modularization is an extremely important part of the design and code-writing process.
That said, here are a few tips about your posted code in particular:
Your function printable is ugly as sin, and therefore impossible to debug or understand.
The number of nested if statements is indicative of design flaws.
You're missing an end brace on your if (isdigit(c)) statement.
Declaring (and especially initializing) multiple variables on the same line is bad form.

Answer 3

Those compile errors surely has a line number associated to them in the error message. Have you tried looking at the line indicated to see what is missing? If that does not help, please post the complete error output from the compiler so that we can se what the error is.

Answer 4

You are missing a few curly braces in your read function.
I redid it here:
void read(char &readStatus, char &var, bool &varStatus)
{
term t; // term variable to push it into the list of terms
char c, lc, sign; // c = current char, lc = lastchar and sign the '+' or '-' sign before a coefficient
int coef, pow; //variables to pass the coef and power to term t
bool coefRead = false, powRead = false; //reading status of coef and power
while (c != '\r') { //we read characters until carriage return
c = getch(); // get the new imputed char
if (tolower(c) == 'r' || tolower(c) == 'q')
{ //if the user inputed r or q we reset the input or quit the program
readStatus = c; //pass current char value to readStatus so the program will know what to do next
return; //aborting the reading process
}
else
{
if (printable(c))
cout << c; //print on screen only the correct characters
if (!coefRead && !powRead) //we set term coef to the inputed value
{
if (isdigit(c))
{
if (isdigit(lc))
coef = coef * 10 + int(c); //if the last char was also a digit we multiply the last value of coef by 10 and add current char
else
{
if (sign == '-')
coef = -(int(c));//if the current coef has '-' before we set coef to it's negative value
else
coef = int(c); //this means a new term's coef is read
} //end else
}//end if isdigit(c)
if (!isdigit(c) && isdigit(lc))
coefRead = true; //if the last char was a digit and we reached the var name we stop reading the coefficient
} //end if
else if (coefRead && !powRead) //after coefficient is read we get the term's varname and power
{
if (isdigit(c))
{ // just like in the case with coefficient we read the power until the current char is not a digit
if (isdigit(lc))
pow = pow * 10 + int(c);
else
pow = int(c);
}
else if (isalpha(c) && isdigit(lc) && !varStatus)
{ //if the last char was a digit and the current not we reached the var name
var = c; //also even though the variable is inputed more than once we save it only once
varStatus = true; //we mark the var name as read
}
else
{
if (isdigit(lc))
powRead = true;
}
} //end else if
else
{
if (c == '+' || c == '-')
{ // if a sign was inputed it means a new term is coming and we push the current term to the list and reset
t.coef = coef; // coefRead and powRead so we can read another term
t.pow = pow;
poly.push_back(t);
sign = c;
coefRead = false;
powRead = false;
}
}
lc = c; // we save the last character
} //end else
} //end while
} //end function
EDIT
I also fixed the print function:
void print(char var)
{
for ( i=poly.begin() ; i != poly.end(); i++ ) { //going through the entire list to retrieve the terms and print them
if (i == poly.end()) { // if we reached the last term
if (i->pow == 0) //if the last term's power is 0 we print only it's coefficient
cout << i->coef;
else
cout << i->coef << var << "^" << i->pow; //otherwise we print both
}
else {
if (i->coef > 0) //if the coef value is positive
cout << i->coef << var << "^" << i->pow << " + "; //we also add the '+' sign
else
cout << i->coef << var << "^" << i->pow << " - "; // otherwise we add '-' sign
}
}
}