c++ - 错误 : expected primary-expression before ‘double’

Question

#include <iostream> 
#include <complex>

using namespace std;

class MyComplex{
  private:
    int real, img;

  public:
    MyComplex();
    MyComplex(int,int);
    ~MyComplex();
    void set(int,int);
    void display();
};

MyComplex::MyComplex(){
  cout << "i'm being constructed (default).\n";
  real=img=0;
}

MyComplex::MyComplex(int r, int i){
  cout << "i'm being constructed (parameterized).\n";
  real=r;
  img=i;
}

MyComplex::~MyComplex(){
  cout << "I'm being destroyed\n";
}

void MyComplex::set(int r, int i){
  real=r;
  img=i;
}

void MyComplex::display(){
  cout << real << "+i" << img << endl;
}



int main(){
  MyComplex c1;
  MyComplex c2(10,-8);
  c1.set(2,9);
  c1.display();
  c2.display();

  cout << "Magnitude"<< double abs(const complex) << endl;
}

第一次上这些论坛，如果我的代码写的很糟糕，我很抱歉，我只是一个初学者。

我在一本书上发现了一项作业，要求您计算复数的大小。

我收到这个错误:

testcomplex.cpp: In function ‘int main()’:
testcomplex.cpp:50:25: ***error: expected primary-expression before ‘double’
   cout << "Magnitude"<< double abs(const complex) << endl;***

Answer 1

您似乎已经编写了函数的声明而不是调用它。假设您实际上有一个名为 abs 的函数，您可以通过简单地将变量传递给它的方括号来调用它:

cout << "Magnitude " << abs(c1) << endl;