Cpp - Write program to compute solutions of quadratic equations

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Requirements

Create a function quadEquation() that calculates the solutions to quadratic equations.

The formula for calculating quadratic equations is shown opposite.

  • Arguments: The coefficients a, b, c and two pointers to both solutions.
  • Returns: false, if no real solution is available, otherwise true.

Test the function by outputting the quadratic equations on the opposite page and their solutions.

Hint

The quadratic equation: a*x*x + b*x + c = 0 has real solutions: 

x1 = (-b + square root of (b - 4ac)) / 2a 
x2 = (-b - square root of (b - 4ac)) / 2a

If the discriminant satisfies: b*b - 4ac >= 0

If the value of (b*b - 4ac) is negative, no real solution exists.

Test values 

Quadratic Equation          Solutions 
   
2x*x  - 2x - 1.5 = 0          x1  = 1.5,  x2  = -0.5 
x*x  - 6x + 9 = 0             x1  = 3.0,  x2  = 3.0 
2x*x  + 2 = 0                 none

Demo

// Defines and calls the function quadEquation(), 
// which computes the solutions of quadratic equations 
//            a*x*x + b*x + c = 0 
// The equation and its solutions are printed by 
// the function printQuadEquation(). 

#include <iostream> 
#include <iomanip> 
#include <string> 
#include <cmath>              // For the square root sqrt() 
using namespace std; 

// Computing solutions: 
bool quadEquation( double a, double b, double c, 
                        double* x1Ptr, double* x2Ptr); 

// Printing the equation and its solutions: 
void printQuadEquation( double a, double b, double c); 

int main() //from  w w w.ja v  a2  s.co m
{ 
    printQuadEquation( 2.0, -2.0, -1.5); 
    printQuadEquation( 1.0, -6.0, 9.0); 
    printQuadEquation( 2.0,  0.0, 2.0); 

    return 0; 
} 
// Prints the equation and its solutions: 
void printQuadEquation( double a, double b, double c) 
{ 
    double x1 = 0.0, x2 = 0.0;           // For solutions 

    cout  << "\nThe quadratic equation:\n\t " 
          << a << "*x*x + " << b << "*x + " <<  c << " = 0" 
          << endl; 

    if( quadEquation( a, b, c, &x1, &x2) ) 
    { 
      cout << "has real solutions:" 
            << "\n\t x1 = " << x1 
            << "\n\t x2 = " << x2 << endl; 
    } 
    else 
      cout << "has no real solutions!" << endl; 

    cout << "\nGo on with return. \n\n"; 
    cin.get(); 
} 

bool quadEquation( double a, double b, double c, 
                         double* x1Ptr, double* x2Ptr) 
// Computes the solutions of the quadratic equation: 
//            a*x*x + b*x + c = 0 
// Stores the solutions in the variables to which 
// x1Ptr and x2Ptr point. 
// Returns: true, if a solution exists, 
//                otherwise false. 
{ 
     bool return_flag = false; 

     double help = b*b - 4*a*c; 

     if( help >= 0)            // There are real solutions. 
     { 
       help = sqrt( help); 

        *x1Ptr = (-b + help) / (2*a); 
        *x2Ptr = (-b - help) / (2*a); 

        return_flag = true; 
     } 
     return return_flag; 
}

Result

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