Program.cs

void Path1(bool a, bool b, bool c, bool d){
    if(a){
        if(b){
            if(c){
                if(d){
                    Console.WriteLine("a->b->c->d");
                }else{
                    Console.WriteLine("a->b->c");
                }
            }else{
                Console.WriteLine("a->b");
            }
        }else{
            Console.WriteLine("a");
        }
    }else{
        Console.WriteLine("");
    }
}

void Path2(bool a, bool b, bool c, bool d){
    if(!a){
        Console.WriteLine("");
        return;
    }

    if(!b){
        Console.WriteLine("a");
        return;
    }

    if(!c){
        Console.WriteLine("a->b");
        return;
    }

    if(!d){
        Console.WriteLine("a->b->c");
        return;
    }

    Console.WriteLine("a->b->c->d");
}

string PathValue(bool a, bool b, bool c, bool d){
    if(!a){
        return "";
    }

    if(!b){
        return "a";
    }

    if(!c){
        return "a->b";
    }

    if(!d){
        return "a->b->c";
    }

    return "a->b->c->d";
}

void Path3(bool a, bool b, bool c, bool d){
    Console.WriteLine(PathValue(a,b,c,d));
}

void Path(bool a, bool b, bool c, bool d){
    if(a){
        if(b){
            if(c){
                if(d){
                    Console.WriteLine("a->b->c");
                }else{
                    
                    Console.WriteLine("a->b->c->d");
                }
            }else{
                Console.WriteLine("a->b");
            }
        }else{
            Console.WriteLine("a");
        }
    }else{
        Console.WriteLine("");
    }
}

// Path(true,true,false,false);


int Calc(char op, int a, int b){
    if(op=='+'){
        return a+b;
    }else if(op=='-'){
        return a-b;
    }else if(op=='*'){
        return a*b;
    }else if(op=='/'){
        try{
            return a/b;
        }catch(DivideByZeroException e){
            throw new Exception("被除数不能为0");
        }
    }else{
        throw new Exception("无效的操作符");
    }
}

int ret = Calc('*', Calc('+',1, Calc('-',3,Calc('/',1,0))), Calc('-',3,Calc('/',1,2)));
Console.WriteLine("ret={0}", ret);