01: #include <math.h>
02:
03: // Function: quadratic
04: // Description: implements the quadratic equation
05: // Parameters: int, int, int: coefficients, float *, float *, pointer to roots
06: // Return: void
07: // Error Avoid division by zero
08: void quadratic(int coeff1, int coeff2, int coeff3, float *root1, float *root2)
09: {
10: if (coeff1 == 0)
11: {
12: // Avoid division by zero
13: *root1 = 0.0;
14: *root2 = 0.0;
15: }
16: else
17: {
18: // Implement quadratic equation
19: *root1=(-coeff2+sqrt((coeff2*coeff2)-(4*coeff1*coeff3)))/(2*coeff1);
20: *root2=(-coeff2-sqrt((coeff2*coeff2)-(4*coeff1*coeff3)))/(2*coeff1);
21: }
22: }
Download the code shown below from here
into a file called main.c in your R3 subdirectory:
01: #include <stdio.h>
02:
03: // Function declaration
04: void quadratic(int coeff1, int coeff2, int coeff3, float *root1, float *root2);
05:
06: // Program entry point
07: int main()
08: {
09: int a, b, c;
10: float r1, r2;
11:
12: printf ("Quadratic Program\n");
13: printf("Enter a: ");
14: scanf("%d", &a);
15: printf("Enter b: ");
16: scanf("%d", &b);
17: printf("Enter c: ");
18: scanf("%d", &c);
19: quadratic(a, b, c, &r1, &r2);
20: printf("Roots are %.2f and %.2f\n", r1, r2);
21: }
Compile the program into an executable called r3, as shown below.
c99 -g -Wall -c r3.c -o r3.o
c99 -g -Wall -c main.c -o main.o
c99 -g -lm r3.o main.o -o r3
To debug the compiled program, type the following command.
Don’t type the stuff after //; those are notes
for your enlightenment.
gdb r3 // start gdb debugger
Use the following debugger commands to run the program and examine variables:
(gdb) set logging on // enable logging to gdb.txt
(gdb) list 20 // listing around line 20
(gdb) break 19 // set breakpoint at line 19 in main.c
(gdb) break 20 // set breakpoint at line 20 in main.c
(gdb) run // run program
Enter integer values for a, b, and c as requested by the program.
(gdb) print a // print value of a
(gdb) print b // print value of b
(gdb) print c // print value of c
(gdb) print r1 // print value of r1
(gdb) print r2 // print value of r2
(gdb) print &r1 // print address of r1
(gdb) print &r2 // print address of r2
(gdb) step // step one line
(gdb) break 21 // set breakpoint at line 21 in r3.c
(gdb) continue // continue to breakpoint just set
(gdb) print root1 // print value of address in root1
(gdb) print root2 // print value of address in root2
(gdb) print *root1 // print value of variable pointed at by root1
(gdb) print *root2 // print value of variable pointed at by root2
(gdb) x root1 // examine memory at address pointed to by root1 (hex)
(gdb) x root2 // examine memory at address pointed to by root1 (hex)
(gdb) x /f root1 // examine memory at address pointed to by root1 (float)
(gdb) x /f root2 // examine memory at address pointed to by root1 (float)
(gdb) info breakpoints // list all breakpoints set above
(gdb) disable 1 // disable first breakpoint
(gdb) info breakpoints // list all breakpoints set above
(gdb) enable 1 // reenable first breakpoint
(gdb) delete 1 // delete first breakpoint
(gdb) info breakpoints // list all breakpoints set above
(gdb) help // show help message command categories
(gdb) help status // show help message for status commands
(gdb) info stack // display stack status
(gdb) info functions // display function status
(gdb) continue // continue to last breakpoint
(gdb) info locals // display local variables status
(gdb) quit // quit debugger
Display the output of your debugging session, show it to the teaching
assistant, and submit the R3.txt file to the Recitation 3 drop box on RamCT.
$ cp gdb.txt R3.txt
$ gedit R3.txt
Challenge: Figure out how to display the contents of r1 and r2 every time the
breakpoint at line 19 in main.c is hit, using the gdb ‘display’ command.