Thread: I need an explanation as to what this code means. (Beginner)

I have a task to find errors in this long line of code in order to correctly calculate the solutions of quadratic equations.

Code:

int main(int argc, char *argv[])
{
    int    validInput, solution_type;
    double a, b, c, root_1, root_2, q;
    
    /***********************
     *  Input / Validation
     ***********************/
    
    /* Check numbers of arguments, and read input */
    validInput = (argc = 4);
    validInput = validInput && scanf(argv[1], "%lf", &a);
    validInput = validInput && scanf(argv[2], "%lf", &b);
    validInput = validInput && scanf(argv[3], "%lf", &c);
    
    /* Calculate roots if input validated */
    if(validInput)
    {
        if(a > 0)

Is a section of the code (the first section). And as you can probably guess, it goes on to calculate for a > 0 etc...

I dont really understand what the validinput section is saying? And a, b and c are never defined so Xcode is just saying a,b,c,root1,root2 are uninitialized and I also dont know what means.

I just need some help really, anything. Do I need to define these values?


-----------

I'll post the whole code below which may help, but i dont expect you to look through for errors and what not:

Code:

int main(int argc, char *argv[])
{
    int    validInput, solution_type;
    double a, b, c, root_1, root_2, q;
    
    /***********************
     *  Input / Validation
     ***********************/
    
    /* Check numbers of arguments, and read input */
    validInput = (argc = 4);
    validInput = validInput && scanf(argv[1], "%lf", &a);
    validInput = validInput && scanf(argv[2], "%lf", &b);
    validInput = validInput && scanf(argv[3], "%lf", &c);
    
    /* Calculate roots if input validated */
    if(validInput)
    {
        if(a > 0)
        {
            /* Quadratic formulas can be used, but only
             if b*b-4*a*c is larger or equal to 0 */
            if(SOLUTION_EXISTS(a,b,c))
            {
                q=sqrt((b*b)-(4*a*c));
                root_1=-0.5*(b+q)/a;
                root_2=-0.5*(b-q)/a;
                if(fabs(root_1-root_2)>ERROR)
                {
                    solution_type=SOLUTION_TYPE_TWO;
                }
                else
                {
                    solution_type=SOLUTION_TYPE_ONE;
                }
            }
            else
            {
                solution_type=SOLUTION_TYPE_ZERO;
            }
        }
        else
        {
            /* If quadratic formulaes do not apply */
            if((b==0)||(c==0))
            {
                solution_type=SOLUTION_TYPE_MANY;
            }
            else if(b==0)
            {
                solution_type=SOLUTION_TYPE_ZERO;
            }
            else if(c==0)
            {
                root_1=0; root_2=0;
                solution_type=SOLUTION_TYPE_ONE;
            }
                else
            {
                    root_1=-(c/b); root_2=0;
                    solution_type=SOLUTION_TYPE_ONE;
                }
            }
            
            /* Print appropriate message */
            if(solution_type==SOLUTION_TYPE_TWO)
                printf("Equation has two solutions: x1=%.3lf x2=%.3lf\n", root_1, root_2);
            else if(solution_type==SOLUTION_TYPE_ONE)
                printf("Equation has one solution: x1=%.3lf\n", root_1);
            else if(solution_type==SOLUTION_TYPE_ZERO)
                printf("Equation has no solutions\n");
            else
                printf("Equation has infinitely many solutions\n");
        }
        else
        {
            printf("**************************************\n");
            printf("* !!!  User input error detected !!! *\n");
            printf("*   Execution method: prog2A a b c   *\n");
            printf("* where a, b and c are real numbers  *\n");
            printf("**************************************\n");
        }

Thanks for the reply, the thing is I've only just started learning C and this is just an online task to improve my C knowledge but I still don't understand the specific definitions of the words people use. For example:

"sufficient command line arguments (hint: there's a bug here that you're probably expected to fix), then parse those command line arguments to be the values of a, b and c (hint: there's a repeated bug in the parsing code)"

When you say there is a bug at the command line argument I don't really know what that means same with parsing part?

Maybe if you give me an example or just highlight the areas that need work that would help. Thanks

Ryan Gregg,
Tell us what the value of validInput should be before and after each line 11-14

Ryan Gregg -

Are you possibly having trouble understanding how it's supposed to work?

Suppose you wanted to add 4 values, w, x, y, and z, and store them in sum.

You could do:

Code:

sum = w + x + y + z;

You could also do this:

Code:

sum = w;
sum = sum + x;
sum = sum + y;
sum = sum + z;

Those values are combined arithmetically (added).

You can also combine logical values, values which are either TRUE or FALSE.

If w, z, y, and x are now logic values, you might have:

Code:

LogicResult = w && x && y && z;     // if w is TRUE AND x is TRUE AND y is TRUE AND z is TRUE, then LogicResult is TRUE.

And similar to the code variation for the arithmetic combination, you can also have:

Code:

LogicResult = w;
LogicResult = LogicResult && x;
LogicResult = LogicResult && y;
LogicResult = LogicResult && z;

The purpose of the validinput section is to test all of the argument values for validity and combine the result into a single value, validInput

Understanding what it is supposed to do should help in finding the errors, if you weren't clear on that.

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