I’m new to C++ and unsure about how to improve this code

Question

The purpose of the following code is to get a random number of 100 nodes and to distribute these nodes randomly in range 500*500 …(X,Y).. this was the first step

#include<iostream>  
#include <fstream>  
#include<cmath>  

using namespace std;  

int  main()   
{  
 const int x = 0, y = 1;   
 int nodes[100][2];    
 ofstream myfile;  
 myfile.open ("example.txt");     
 myfile << "Writing this to a file.\n";  

 for (int i=0; i<100 ;i++)  
 {     
      nodes[i][x] = rand() % 501;    
      nodes[i][y] = rand() % 501;  
      myfile <<nodes[i][x]<<" "<<nodes[i][y];  
 }

 myfile.close();
}

now the next step is to improve this code to distribute these nodes in order ( "Imust divide both xy_coordinates as : x= 0-100-200-300-400-500 & y=0-100-200-300-400-500) next is to distribute the nodes (regardless number of nodes) in order range Starting from (0,100 )….(100,100)..(100,200)…….untile i reach the last point (500,500),, ")

I’m really confused of how to do it correctly I start to think to define 2 dimensional array , and then to define 2 for loops

    enter code here
     Int no_nodes=100;  
    Int  XY_coordinate [500][500];  
     For (int i=0;i<no_nodes; i++)  
  {  
 For (int j=0;j<no_nodes; j++) 

---

As shown in the image the x and y axis will be divided in to 5*5 , so I will have 25 grids Starting the axis from 0-99-199-299 until 499 ,what I’m trying to do is to distribute 4 nodes in each “100*100” grid I try to do it by rewrite the code, but I get an error and I could not understand it

THE ERROR IS :" 1 IntelliSense: expression preceding parentheses of apparent call must have (pointer-to-) function type"

how can i fix it ?

   #include <iostream>  
   #include <fstream>  
   #include <cmath>  

    using namespace std;  



     int  main()   

     {  
 ofstream myfile;  
       myfile.open ("example.txt");  
       myfile << "Writing this to a file.\n"; 


       int miny=0,max_y=99;
       for(int i=0;i<5;i++)
       {
int minx=0,max_x=99;
       for(int j=0;j<5;j++)
      {
for(int k=0;k<=4;k++)
{
int     x=(minx+rand()*10(max_x +1)%(max_x - minx+1));
int     y=(miny+rand()*10(max_y +1)%(max_y - miny+1));
}
minx=max_x+1;
max_x=max_x+100;
     }
     miny=max_y+1;
     max_y=max_y+100;
     }
      }

Answer 1

At least for now, I'm just going to look at coding style.

#include<iostream>  
#include <fstream>  
#include<cmath>  

I'd always put a space before the <. Never putting a space there is somewhat acceptable too. Changing from one to the other is not so good.

using namespace std;  

This should almost always be avoided. It's generally better to include the namespace qualifiers as needed, or just use using declarations to bring in the names you really need.

int  main()   
{  
 const int x = 0, y = 1;   
 int nodes[100][2];

Here you're basically using a 2D array to simulate an array of 2D points. I'd rather see 2D points. Since you're going to create points with values, let's include a constructor to make that a little simpler:

struct point { 
    int x, y;

    point(int x, int y) : x(x), y(y) {}
};

Since you're also writing these values out to a stream, let's overload operator<< for the type:

std::ostream &operator<<(std::ostream &os, point const &p) { 
    return os << p.x << " " << p.y;
}

I'd also rather see a vector than an array:

std::vector<point> nodes;

When it comes to creating and initializing objects:

 ofstream myfile;  
 myfile.open ("example.txt");

...prefer to create an object initialized over creating it uninitialized, and initializing it to a useful state later:

std::ofstream myfile("example.txt");

This doesn't make a huge difference in this case, but I'd try to cultivate the habit -- in other cases it makes a much bigger difference (and even in this case, it's at least slightly helpful).

 for (int i=0; i<100 ;i++)  
 {     
     nodes[i][x] = rand() % 501;    
     nodes[i][y] = rand() % 501;  
     myfile <<nodes[i][x]<<" "<<nodes[i][y];  

With the definitions we have for point, nodes and operator<< we have above, this loop becomes something like:

for (inti=0; i<100; i++) {
    nodes.push_back(point(rand() % 501, rand() % 501));
    myfile << nodes[i];
}

You might also want to consider using algorithms for the job instead:

std::generate_n(std::back_inserter(nodes), 100, []{return node(rand()%501, rand()%501); });
std::copy(nodes.begin(), nodes.end(), std::ostream_iterator<node>(myfile, "\n"));

Finally (well, final comment on this point, anyway) % doesn't produce a particularly good distribution of numbers either. You might want to consider another method.

myfile.close();

I generally prefer to let RAII do its job, so manually closing a file is unnecessary. Better to let it close automatically as the stream object goes out of scope.