请编写代表复数的类ComplexNum和该类的测试类ComplexTest。具体要求如下：

根据你的说明貌似应该是用java或者c#实现。因为c++的main函数不是写在类里的
现提供一个java版本的实现仅供参考：
public class ComplexNum {
private int a;
private int b;

public ComplexNum() {
this(0, 0);
}

public ComplexNum(int a, int b) {
this.a = a;
this.b = b;
}

public int getA() {
return a;
}

public int getB() {
return b;
}

public ComplexNum sub(ComplexNum val) {
return new ComplexNum(this.a - val.a, this.b - val.b);
}

}

class ComplexTest {
public static void main(String[] args) {
ComplexNum n1 = new ComplexNum();
ComplexNum n2 = new ComplexNum(3, 4);
System.out.printf("n1 = %d + %di\n",n1.getA(),n1.getB());
System.out.printf("n2 = %d + %di\n",n2.getA(),n2.getB());
ComplexNum n3= n1.sub(n2);
System.out.printf("n2 = %d + %di\n",n3.getA(),n3.getB());

}
}