Quadratic Equation Solution in C Language

Program Code:
#include<stdio.h>
#include<math.h>

int main(){
  float a,b,c;
  float d,x1,x2;
  char redo;

  printf("Enter a, b and c of quadratic equation: ");
  scanf("%f%f%f",&a,&b,&c);
 
  d = b * b - 4 * a * c;
 
  if(d < 0){
    printf("Roots are complex number.\n");

    printf("Roots of quadratic equation are: ");
    printf("%.3f%+.3fi",-b/(2*a),sqrt(-d)/(2*a));
    printf(", %.3f%+.3fi",-b/(2*a),-sqrt(-d)/(2*a));
 
    return 0;
  }
  else if(d==0){
   printf("Both roots are equal.\n");

   x1 = -b /(2* a);
   printf("Root of quadratic equation is: %.3f ",x1);

   return 0;
  }
  else{
   printf("Roots are real numbers.\n");
 
   x1 = ( -b + sqrt(d)) / (2* a);
   x2 = ( -b - sqrt(d)) / (2* a);
   printf("Roots of quadratic equation are: %.3f , %.3f",x1,x2);
  }
 
 
  return 0;
}