C++ 实例二次方程 ax2+bx+c = 0 (其中a≠0），a 是二次项系数，bx 叫作一次项，b是一次项系数；c叫作常数项。
x 的值为：
根的判别式
实例
#include <iostream>#include <cmath>using namespace std; int main() { float a, b, c, x1, x2, discriminant, realPart, imaginaryPart; cout << "输入 a, b 和 c: "; cin >> a >> b >> c; discriminant = b*b - 4*a*c; if (discriminant > 0) { x1 = (-b + sqrt(discriminant)) / (2*a); x2 = (-b - sqrt(discriminant)) / (2*a); cout << "Roots are real and different." << endl; cout << "x1 = " << x1 << endl; cout << "x2 = " << x2 << endl; } else if (discriminant == 0) { cout << "实根相同：" << endl; x1 = (-b + sqrt(discriminant)) / (2*a); cout << "x1 = x2 =" << x1 << endl; } else { realPart = -b/(2*a); imaginaryPart =sqrt(-discriminant)/(2*a); cout << "实根不同：" << endl; cout << "x1 = " << realPart << "+" << imaginaryPart << "i" << endl; cout << "x2 = " << realPart << "-" << imaginaryPart << "i" << endl; } return 0;}
以上程序执行输出结果为：
输入 a, b 和 c: 451实根不同：x1 = -0.25x2 = -1