Hmmm...I decided to write a function which intiated two iterators b and e and then use the find_if function and the isdigit function as the predicate to locate a digit. Iterators b and e will search for the beginning of digit and end of digit respectively and copy what is between both iterators into a vector. I then placed all elements of the vector into an array .

My aim is to split a quadratic equation
ax^2 + bx + c = 0,
and pull out a, b and c.
My code above is expected to use iterators b1 and e1 to go through the string and based on my function coeff_b and coeff_e will take these out and put them into a vector called coeff1; at that point I would prefer to use an array. How do I place the vector values into an array?

As i figured, the function to split the string into an array and then use the values in my array to do computations is least I think it so. Here's what I have. My explanations follow:

//this first piece initializes the string. Basically it splits the string and places it into a vector called coeff1. Mt delimiters are +, - and = and this will be implemented in my coeff_b function which I'm having problems with. Does this even make sense?
string s;
vector<string> find_coeff (const string& s)
vector<string> coeff1;
typedef string::const iterator it;
it b1 = s.begin ()
it b2 = s.end ()

while (b1 !=e1) {
b1 = coeff_b (b1, e1)

if (b1 !=e1) {
it b2 = coeff_e (b1, e1)

coeff1.push_back(b1, b2)
b1 = b2;
return coeff1;

//I then have to write functions for the predicates coeff_b and coeff_e

coeff_e(b1, e1)
string :: const_iterator
coeff_e (const_iterator b1, const_iterator e1)
return find_if (b1, e1, v_coeff)

//Now I need to write a function for v_coeff predicate to return false if the characters entered are not valid. Can you tell me if this makes sense?

bool coeff2 (char d)
static const string val1 = "0 1 2 3 4 5 6 7 8 9"
return (isalnum (c) || find val1.begin (), val1.end (), d) !=val1.end() );

Hi, I have another issue. Thanks, by the way Val. I'm currently working on a function to extract a, b and c from the string and place it in an array. Let's hope it works.

My issue is this:
Provided I've written my main function Root_Quadratic, how do I tell the program that the quadratic equation to be solved is in the element argv[2]? Obviously
string quadratic = ax^2 + bx + c;
argv[2] = quadratic
wouldn't work.

I in my main function I called for Root_Quadratic() when argv[1] is "-r" ( I used strcmp to do this.) So my thinking process is this:
-r is entered, the function is called, program goes to this function and should execute it. the quadratic is in the next element in the arg array at argv[2], how do I tell my program that?

I know I have a lot of question of something that might be simple, but I'm learning here. And resources are limited where I am right now.

I should have given an example, but yes...your example says it. The user types the entire equation e.g. 2x^2 + 3x + 5.

Basically, what I'm thinking is I need to come up with some kind of code which, when the user types in the quadratic equation, will identify a as the coefficient of x^2 (in this case 2), b as the coefficient of x (in this case 3) and c as the constant (=5). The program should then place it into the array [a b c] and then in the function, a pointer will extract the elements and manipulate them into the computational formula. It sound allright, but the code is heavy. I just cant figure it out, and I'm not too sure that an array would work. Maybe a vector?

What about the other aspects? Integral and differential of the equation? Any thoughts?

Thanks Val. I understand when you have just the COEFFICIENTS of a, b and c being entered by the user. However, the specs required the ENTIRE quadratic equation to be entered by the user i.e. the inclusion of a single variable be it x or p or q or whatever. Any suggestions?

On another note, can one suggest how to go about writing functions to integrate and differentiate a quadratic equation/expression. This would involve both coefficient and variable, so once again any suggestions.

Maybe I can write an algorithm (well sort of) to explain what I\ve got so far, in terms of how this thing works.

int main (int argc, char* argv[])  <-- obvious by now

//I'm thinking to place the coefficients a, b and c into an array of size 3 and when the command is called, the program will use the values from here to work out the roots.

//Initialize variables here

int coeff[3];
int quadratic;

if(strcmp (argv[1], "-help") == 0) {
cout << help menu <<endl;    (the help menu is not available to me right now, so
we'll just work with the bad syntax

if(strcmp (argv[1], "-r") == 0) {argv[2] = quadratic ??

(at this point I would insert the function to find the roots of the quadratic??)

Herein lies two problems.

  1. The problem I mentioned before about the values a, b and c.
  2. Does the line if placed in bold make any sense?

The code is basic. (I dont have it with me. My apologies.)

void Root_Quadratic ();

int a;
int b;
int c;
double r1;
double rt2;
double d_crim;

d_crim = pow(b,2) - (4 * a * c);
r1 = (-b + sqrt(d_crim)) / (2 * a);
r2 = (-b - sqrt(d_crim)) / (2 * a);

cout << r1 << r2 << endl;

Not that I'm recalling from memory, so there may be some stuff I'm forgetting, but I believe I have the gist of it. Ignore the syntactical errors I made. My issue is that the function declares a, b and c as integers and so on. But what do I need to write again such that when the command -r at argv[1] and the quadratic equation at argv[2] are typed and this function is called, the program will automatically know which values of the quadratic equation the user typed are a,b and c.

Think of it this way:
It's similar to other simple programs which find the root of a quadratic with the exception that there is no

cout<< "Enter the value of a:" <<endl;
cout<< "Enter the value of b:" <<endl;
cout<< "Enter the value of c:" <<endl;

And then the user enters these values and the program uses a formula (similar to that above) and computes two roots and then displays these roots. My code is similar WITH THE EXCEPTION that the user is not prompted to enter these values hence the program must know which ...

Thanks Val. That will work finely. However, when I wrote my code for my quadratic, I neglected something quite important, actually. Please bear in mind that I am a beginner at this. Let me see if I can explain.

The first argument will automatically be the program name, followed by the command the use will type in. I organized it such that when the use types in "-r", the program will call my function to calculate the roots. Here is my problem. I'm not sure how to write the code such that the program will automatically read the values of a, b and c and do the required computation. My function (which I've aptly named Root_Quadratic") basically acknowledges integers a, b and c and then via an if loop computes the roots and displays the roots. But the step to get my program to KNOW which values are a, b and c, I'm not sure. Remember that I'm writing the entire quadratic equation as my third argument (argv[2]). Once again, some guides will be quite helpful here. I know I'm missing something quite simple, but I just cant figure it out.

Hello all,

My assignment is to write a quadratic equation solver. I have written the function, and it compiles well. However that is not the issue. The requirements are that it follows a command line interface specification as follows:

<program name> -r <quadratic equation>

In other words, the user is to enter "-r" followed by the equation, and the program will then output the roots as two numbers on the next line, and that's it. That means I can't have any other expressions like "Enter the value of a..." or "Enter the value of b..." and then cin my b variable. How do I write the piece of code so that all the user has to do is type "-r" and then the equation, and this will call my function and output the results? Any suggestions or guides..?