Here's a C program to find the roots of a quadratic equation with output and proper explanation. This program uses Switch Case Condition, Break, IF-Else and Math.H Header File to use functions like pow() and sqrt().

**General format of second degree quadratic equation -**

Fig 1: Second Degree Quadratic Equation. |

**Roots of quadratic equation are -**

Fig 2: Roots of Quadratic Equation. |

**And discriminant can be calculated as -**

Fig 3: Discriminant of Quadratic Equation. |

# include <stdio.h> # include <conio.h> # includevoid main() { float a, b, c, d, real, imag, r1, r2, n ; int k ; clrscr() ; printf("Enter the values of A, B & C : ") ; scanf("%f %f %f", &a, &b, &c) ; if(a != 0) { d = b * b - 4 * a * c ; if(d < 0) k = 1 ; if(d == 0) k = 2 ; if(d > 0) k = 3; switch(k) { case 1 : printf("\nRoots are imaginary\n") ; real = - b / (2 * a) ; d = - d ; n = pow((double) d, (double) 0.5) ; imag = n / (2 * a) ; printf("\nr1 = %7.2f + j%7.2f", real, imag) ; printf("\nr2 = %7.2f - j%7.2f", real, imag) ; break ; case 2 : printf("\nRoots are real and equal\n") ; r1 = - b / (2 * a) ; printf("\nr1 = r2 = %7.2f", r1) ; break ; case 3 : printf("\nRoots are real and unequal\n") ; r1 = (- b + sqrt((double) d)) / (2 * a) ; r2 = (- b - sqrt((double) d)) / (2 * a) ; printf("\nr1 = %7.2f",r1) ; printf("\nr2 = %7.2f",r2) ; break ; } } else printf("\nEquation is linear") ; getch() ; }

**Output of above program is**

Enter the values of A, B & C : 1.0 2.0 7.0

Roots are imaginary

r1 = -1.00 + j 2.45

r2 = -1.00 - j 2.45

Enter the values of A, B & C : 1.0 2.0 1.0

Roots are real and equal

r1 = r2 = -1.00

**Explanation of above program**

Variables used in this program -

- a, b, c - are the coefficients of quadratic equation (see fig 1).
- d - is the discriminant of quadratic equation (see fig 3).
- real and imag - are the variables used only in the case when the roots of quadratic equation are imaginary. In that case real will contain the real part of the root and imag will contain the imaginary part of the root.
- r1 and r2 - are the two roots in case the roots of the equation are real.
- k - is used to switch between different cases based on the value of discriminant.

First we ask the user to enter the value of A, B and C coefficients. Next we check whether the value of variable

**a**is zero or not using IF-Else condition. If the value of**a**is zero that means our equation is linear in nature i.e.**bx + c**and hence we print it out in the else part and terminate the program. Otherwise in the if part, we calculate the roots of the equation.
Inside IF, we first calculate the discriminant and store it in variable

**d**. After calculating value of d we can decide which case to execute in the switch case condition -- If d < 0 i.e. roots are imaginary. So Case 1 is executed.
- If d = 0 i.e. roots are real and equal. So Case 2 is executed.
- If d > 0 i.e. roots are real and unequal. So Case 3 is executed.

Once the value of d is calculated the right case according to the value of d is executed and the roots are calculated according to the formula (see fig 2).

Note:If you notice in the linen = pow((double) d, (double) 0.5), you must be wondering what is the purpose of writing(double) d and(double) 0.5instead of justd and 0.5. The reason is that we're casting the value of that variable. When we first declared the variable d it was of the type float. But now we want to use its value as a double so we're casting the value of variable d from type float to double. The same case is with the value 0.5.

Hi Tanmay,

So bloody thorough! Ah! So happy and blessed out! I feel redeemed by reading out Finding Roots of Quadratic Equation in C | C Program. Keep up the good work!

Is there any API in C to check if any of the Unix service is up or down.

Like I want to know if syslog service is up and down in C program.

if down how to bring it up using C program?

In C and C++, any time you need a void pointer, you can use another pointer type. For example, if you have a char*, you can pass it to a function that expects a void*. You don’t even need to cast it. In C (but not in C++), you can use a void* any time you need any kind of pointer, without casting. (In C++, you need to cast it).

A void pointer is used for working with raw memory or for passing a pointer to an unspecified type.

Some C code operates on raw memory. When C was first invented, character pointers (char *) were used for that. Then people started getting confused about when a character pointer was a string, when it was a character array, and when it was raw memory.

Awesome! Thanks for putting this all in one place. Very useful!

Regards,

Jennifa

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