::Need help Please:: using If & Switch in Quadratic equation.

internetbug · #1 07-Apr-2005, 15:10

i need help for this program.

in the following program, i need help using switch, so that i could choose all the possible roots for the program. such as 1) real roots
2) imaginary roots
3) repeated roots
4) exits (default)

the program.

CPP / C++ / C Code:

#include <stdio.h>
#include <math.h>
    int main(void) {
    	double a, b, c, d, x1, x2, x;
    	printf(" Quadratic Equation ax^2+bx+c=0 \n");
    	printf("**************************************\n");
    	printf("\na = ");
    	scanf("%lf", &a);
    	printf("b = ");
    	scanf("%lf", &b);
    	printf("c = ");
    	scanf("%lf", &c);

        	if(a==0) {

            		if(b==0 && c!=0) {
            			printf("\n**************************************\n");
            			printf("The equation hasn't root(s)\n\n");
            		}

                		else if(b!=0) {
                			x=-c/b;
                			printf("\n**************************************\n");
                			printf("X=%lf\n\n", x);
                		}


                    		else if(b==0 && c==0) {
                    			printf("\n**************************************\n");
                    			printf("The equation has infinite roots\n\n");
                    		}
                    	}

                        	else {
                        		d=(b*b)-(4*a*c);


                            		if(d<0) {
                            			printf("\n**************************************\n");
                            			printf("The equation hasn't root(s)\n\n");
                            		}

                                		else if(d==0) {
                                			x=-b/(2*a);
                                			printf("\n**************************************\n");
                                			printf("X = %lf\n\n", x);
                                		}


                                    		else if(d>0) {
                                    			x=sqrt(d);
                                    			x1=(-b+x)/(2*a); x2=(-b-x)/(2*a);
                                    			printf("\n**************************************\n");
                                    			printf("\nX1 = %lf\nX2 = %lf\n\n", x1, x2);
                                    		}
                                    	}
                                    	return 0;
                                }

internetbug · #2 07-Apr-2005, 15:34

Need three choices for the switch:
1) real roots
2) imaginary roots
3) repeated roots
4) exits (default)

Stack Overflow · #3 07-Apr-2005, 16:04

Hello,

The switch statement
The switch statement is a multi-way decision that tests whether an expression matches one of a number or constant integer values, and branches accordingly:

CPP / C++ / C Code:

switch (expression) {
	case const-expr:	statements
	case const-expr:	statements
	default:	statements
}

Each case is labeled by one or more integer-valued constant expressions. If a case matches the expression value, execution starts at that case. All case expressions must be different. The case labeled default is executed if none of the other cases are satisfied. A default is optional; if it isn't there and if none of the cases match, no action at all takes place. Cases and the default clause can occur in any order.

The break statement causes an immediate exit from the switch. Because cases serve just a labels, after the code or one case is done, execution falls through to the next unless you take explicit action to escape. break and return are the most common ways to leave a switch. A break statement can also be used to force an immediate exit from while, for, and do loops.

Here's an example of using a switch statement in your program:

CPP / C++ / C Code:

#include <stdio.h>
#include <math.h>

/* Prototypes */
void realRoots(double, double, double);
void imaginaryRoots(double, double, double);

int main() {
	/* Local variables */
	int option;
	double a, b, c, d;

	printf(" Quadratic Equation ax^2+bx+c=0 \n");
	printf("**************************************\n");

	/* Print list */
	printf("\n1) Real roots\n");
	printf("2) Imaginary roots\n");
	printf("3) Repeated roots\n");
	printf("4) Exit\n");

	/* Get option from user */
	scanf("%d", &option);

	printf("**************************************\n");

	/* Get a, b, and c from user */
	printf("\na = ");
	scanf("%lf", &a);
	printf("b = ");
	scanf("%lf", &b);
	printf("c = ");
	scanf("%lf", &c);

	/* Calculate determinant */
	d = (b * b) - (4 * a * c);
	
	/* Use switch statement */
	switch(option) {
	/* If 1 was selected */
	case 1:
		realRoots(a, b, sqrt(d));
		break;
	/* If 2 was selected */
	case 2:
		imaginaryRoots(a, b, sqrt(-d));
		break;
	/* If 3 was selected */
	case 3:
		break;
	/* If 4 was selected */
	case 4: 
		break;
	}

	/* End program */
	return 0;
}

/* Evaluate real roots */
void realRoots(double a, double b, double d) {
	/* Calculate */
	double firstRoot = (-b/(2 * a)) + (d/(2 * a));
	double secondRoot = (-b/(2 * a)) - (d/(2 * a));
	/* Print */
	printf("\nFirst Real Root: \t%lf\n", firstRoot);
	printf("\nSecond Real Root: \t%lf\n", secondRoot);
}

/* Evaluate imaginary roots */
void imaginaryRoots(double a, double b, double d) {
	/* Calculate */
	double x = 2 * a;
	double first_term = (-b)/x;
	double second_term = (d)/x;
	/* Print */
	if(second_term >= 0) {
		printf("\nFirst Imaginary Root: \t%lf + %lfi\n", first_term, second_term);
		printf("\nSecond Imaginary Root: \t%lf - %lfi\n", first_term, second_term);
	}else {
		second_term = -(second_term);
		printf("\nFirst Imaginary Root: \t%lf + %lfi\n", first_term, second_term);
		printf("\nSecond Imaginary Root: \t%lf - %lfi\n", first_term, second_term);
	}
}

I didn't add the Repeated roots function, so you can have something to do. I also split the program into different functions. If you have questions, please feel free to ask.

- Stack Overflow

davekw7x · #4 07-Apr-2005, 17:38

Quote:

Originally Posted by internetbug

i need help for this program.

in the following program, i need help using switch, so that i could choose all the possible roots for the program. such as 1) real roots
2) imaginary roots

If a is equal to zero, it's not a quadratic equation and you have handled that.

For a not equal to zero,your conditional statements (d < 0), (d == 0), and (d > 0), tell you whether there are complex roots, repeated real roots, and distinct real roots, respectively.

Why do you think you need a switch statement? What value would that add to your program?

Regards,

Dave

davekw7x · #5 07-Apr-2005, 17:44

Quote:

Originally Posted by Stack Overflow

Hello,

Here's an example of using a switch statement in your program:

How is the user supposed to know the type of roots his equation has? What if he gives the coefficients for an equation that has complex roots, but tells the program to find real roots (or vice versa)?

Shouldn't the program at least check before trying to take the square root of a negative number? But, wait a minute: if the program can check to see whether the roots are real or complex, then why make the user tell it in the first place? I guess I missed the point.

Regards,

Dave

internetbug · #6 07-Apr-2005, 18:03

Quote:

Originally Posted by davekw7x

If a is equal to zero, it's not a quadratic equation and you have handled that.

For a not equal to zero,your conditional statements (d < 0), (d == 0), and (d > 0), tell you whether there are complex roots, repeated real roots, and distinct real roots, respectively.

Why do you think you need a switch statement? What value would that add to your program?

Regards,

Dave

you are right. but this is a Hw problem, and i really needed help using switch statements, cause we had to use switch statements for this problem, to make a choice kind a problem.

thank you Stack overflow for the help. it works.

davekw7x · #7 07-Apr-2005, 18:36

Quote:

Originally Posted by internetbug

you are right. but this is a Hw problem, and i really needed help using switch statements, cause we had to use switch statements for this problem, to make a choice kind a problem.

thank you Stack overflow for the help. it works.

At least I was correct in my response to Stack Overflow:

Quote:

Originally Posted by davekw7x

I guess I missed the point.

Sorry.

Regards,

Dave

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