C#编程：定义一个复数类,实现复数的简单加法运算,并能显示结果.

class fs
{
public double a;//实部
public double b;//虚部
//加法
public fs add(fs fs1)
{
fs fs_temp = new fs();
fs_temp.a = this.a + fs1.a;
fs_temp.b = this.b + fs1.b;
return fs_temp;
}
//减法
public fs jf(fs fs1)
{
fs fs_temp = new fs();
fs_temp.a = this.a - fs1.a;
fs_temp.b = this.b - fs1.b;
return fs_temp;
}
public string ToString()
{
if(b==0){
return "" + a;
}
else if (a == 0)
{
return b + "i";
}
else
{
return a + "+" + b + "i";
}
}