CS 1713, Assignment 1, Spring 1998, due January 20
Copy Program, Quadratic Equations
The assignment: Copy the program, compile and run it, and turn in a listing and results of the run. 
/* Name:       Insert your name here
 * Date:       Insert the due date here
 * Course:     CS 1713 Section n
 * Subject:    Calculate the roots of a quadratic equation.
 * Algorithm:  Read coefficients from the terminal. Use the quadratic formula.
 *             Only real roots are calculated.
 * Input:      Enter three coefficients in double format.
 * Output:     If the roots are real, display them.
 *             Otherwise display an error message.
 */
#include <stdio.h>
#include <stdlib.h>
#include <math.h>

void main(int argc, char *argv[])
{
    double a0, a1, a2;  /* coefficients in a2 x^2 + a1 x + a0 = 0 */
    double discriminant;  /* a1*a1 - 4*a2*a0 */
    double root1, root2;  /* the two roots of the equation */
    /* prompt for the coefficients, if not on command line */
    if (argc == 1) {
        fprintf(stdout, "Solving a2 x^2 + a1 x + a0 = 0\n");
        fprintf(stdout, "Enter a2, a1, a0 (in order): ");
        scanf("%lf %lf %lf", &a2, &a1, &a0);
    }
    else if (argc == 4) {  /* get coefficients from command line */
        a2 = atof(argv[1]);
        a1 = atof(argv[2]);
        a0 = atof(argv[3]);
    }
    else { 
          fprintf(stderr, "%s requires 0 or 3 arguments\n", argv[0]);
        exit(1);
    }
    fprintf(stdout, "Solving %5.3f x^2 + %5.3f x + %5.3f = 0\n",
          a2, a1, a0);
    if (a2 == 0.0) {  /* this is a linear equation (no quadratic term) */
        fprintf(stderr, "a2 must not be 0 in a quadratic equation\n");
        exit(1);
    }
    discriminant = a1*a1 - 4.0*a0*a2;
    if (discriminant < 0.0) {
        fprintf(stderr, "Roots are complex numbers\n");
        exit(1);
    }
    /* calculate roots and output them */
    root1 = (-a1 + sqrt(discriminant))/(2.0*a2);
    root2 = (-a1 - sqrt(discriminant))/(2.0*a2);
    fprintf(stdout, "Roots: %5.3f, %5.3f\n", root1, root2);
    exit(0);
}
What to do:  ( In the text that follows, boldface is what you should enter at the keyboard.)
1.      Connect to the machine: look for a terminal with the "local>" prompt, or connect to UTSA by 
modem.  You may have to type RETURN to get the prompt:        Local> c runner
        You should now get the prompt:         login:
2.      Carry out the login to your account: type in your account name:      login: YourAccountName
        You should get the prompt:     Password:
        Next enter your password, initiallyyour 9-digit SSN without hyphens:     Password: YourSSN
3.      You are now on the system. The first time you will be asked to choose a new password.  The new 
password must be 6 to 8 characters long, and must contain at least 2 alphabetic  characters and at least 
1 numeric or special character. The system will prompt you for your old password (your SSN) and 
your new password (twice, to check that you have it correct).  You will see the following on the 
screen:
                        Your password has expired.  Choose a new one.
                        Old password: YourSSN
                        New password: YourNewPassword
                        Re-enter new password: YourNewPassword
        (Blanks and upper or lower-case letters count in these passwords and elsewhere.  Do not forget your 
new password.)  You are now on the system and should get the system prompt:   runner%
4.      Now create a file called roots.c which will contain the copy program for the first assignment, 
listed above.  (This program reads in 3 numbers that are used as the coefficients of a quadratic 
equation.  The program then calculates and prints the roots of this equation.)  Read about the vi editor 
in the UNIX Primer book.  To use vi, type:      runner% vi roots.c
5.      When you have finished typing the program, you should first check it for correctness with the lint 
utility:            runner% lint -m -u roots.c -lm
        (Don't leave off the "magic" hyphen-el-em at the end.)
        If you have typed in the program correctly, you should get the following messages from lint, which 
you can ignore for now:
                        function returns value which is always ignored
                        fprintf     scanf           
        You must carefully type exactly the characters given for the program.  If there are any typing 
mistakes, you will probably get error messages from lint.
6.      Next you should compile the program roots.c to produce an executable module called roots.  
For this type the command:       runner% cc -o roots roots.c -lm
        There are a number of "magic" parts to this command which must be just right.  The "cc" invokes the 
C compiler.  The "-o roots" says to name the executable file "roots".   Finally the same "-lm" 
as with lint above tells the system where to find the sqrt function in roots.c, that calculates the 
square root.  Everything must be exactly right, so that it must be a lower-case "Oh" in "-o" and it 
must be a lower-case "El" in "-lm", and not a zero or a one.  There should be no messages in 
response to this command.  If you have not typed in the  program correctly, then as with lint, you will 
probably get error messages.
7.      Now you can try executing your program, in one of two ways, either with the three numbers  on the 
same line that starts up the program, or with the three numbers typed later.  In Unix we execute a file 
by just typing the name of the file.  After execution completes you will get the "runner%" prompt 
again.          runner% roots 1.0 -2.0 -3.0
                        Solving 1.000 x^2 + -2.000 x + -3.000 = 0
                        Roots: 3.000, -1.000
                        runner% roots
                        Solving a2 x^2 + a1 x + a0 = 0
                        Enter a2, a1, a0 (in order): 1.0 -2.0 -3.0
                        Solving 1.000 x^2 + -2.000 x + -3.000 = 0
                        Roots: 3.000, -1.000
                        runner% 
        You should try entries that result in complex roots, and an entry with first coefficient zero.
8.      When you have gotten this far, you can produce a listing to hand in.  For this purpose, you should use 
the script command, which inserts every character that appears on the screen into a file named 
"typescript".  Script is terminated with Control-d (hold the Control key down and type "d").  
Inside script you should type "cat roots.c" to cause your program text to appear on the screen.  
Then you should execute the program with inputs as above.  A sample session might look like:
                        runner% script
                        Script started, file is typescript
                        runner% cat roots.c
                        /* Name:       Insert your name here
                        * Date:       Insert the due date here
                            ... (lines omitted)
                              exit(0);
                        }
                        runner% roots 1.0 -2.0 -3.0
                        Solving 1.000 x^2 + -2.000 x + -3.000 = 0
                        Roots: 3.000, -1.000
                        runner% roots
                        Solving a2 x^2 + a1 x + a0 = 0
                        Enter a2, a1, a0 (in order): 1.0 -2.0 -3.0
                        Solving 1.000 x^2 + -2.000 x + -3.000 = 0
                        Roots: 3.000, -1.000
                        runner% Control-d Script done, file is typescript
9.      Now finally you can get a printout to hand in for this assignment by typing:
                        runner% lp -d SCF1 typescript
                Put your name at the front of this listing and hand it in on the due date.
10.     When you are done you should logout by typing exit:     runner% exitnext1.cs.utsa.edu>