Write a Stub for the Following Function Prototype

Essay

Write a stub for the following function prototype:
double root( double a,double b,double c,int i);
// Precondition: a != 0 and a,b,c are coefficients of
// a quadratic equation a*x*x + b*x + c = 0 The value
// of i is either +1 or -1 to choose which root.
// Postcondition: return value,x,satisfies the
// equation a*x*x + b*x + c = 0