Converting C++ code to C, array of structs - c++

Question

I'm converting C++ code to C for an exercise (we are just learning c++ now), and I am lost at this part.
First, the c++ code:
Point()
{
x = y = 0;
}
main()
{
const int N = 200;
Point *A = new Point[N], sum;
}
Here's my C version of it:
struct Point //constructor
{
int x;
int y;
} Point;
main()
{
int N = 200;
Point* A = malloc(N * sizeof(*Point[]));
}
That should give you an idea of what I'm trying to do. Questions:
Is sum in the C++ code the C++ sum function, or is it aPointstruct`?
For allocating the memory in C, I don't think my method works. Should I do a for loop where it mallocs each index of A[]? (A should be an array of Point structs).
Any assistance would be greatly appreciated.
EDIT: Got asked for the context of the code.
Here's the whole C++ program:
#include <iostream>
// a point on the integer grid
struct Point
{
// constructor
Point()
{
x = y = 0;
}
// add point componentwise
void add(const Point &p)
{
x += p.x;
y += p.y;
}
// print to standard output
void print() const
{
std::cout << "[" << x << "," << y << "]" << std::endl;
}
// data
int x, y;
};
int main()
{
const int N = 200;
Point *A = new Point[N], sum;
for (int i=0; i < N; ++i) {
sum.print();
A[i].x = i; A[i].y = -i;
sum.add(A[i]);
}
sum.print();
delete [] A;
}
Ultimately, I have to emulate that in C. Currently stuck at the question I asked: re: what does that line do. I have since figured out that I need to make a struct of Point called sum, and print that after running the add function on all its members.

Answer 1

In your C version:
struct Point //constructor
{
int x;
int y;
} Point;
should be:
typedef struct //constructor
{
int x;
int y;
} Point;
Because in your case, you defined a global variable named Point.
And, the C programming language has the const keyword as C++ as well, so you can do this in the C language:
const int N = 200;
And the C++ code:
Point *A = new Point[N], sum;
In C version, should be:
Point *A = malloc(N * sizeof(Point)), sum;
But in this version, the memory isn't initialized by zero.
You can use the calloc function instead of the malloc to allocate memory and initialize it with zero:
Point *A = calloc(N, sizeof(Point)), sum;
Then back to your question:
Is sum in the c++ code the c++ sum function, or is it a Point struct?
It is a Point type variable.
For allocating the memory in C, I don't think my method works. Should I do a for loop where it mallocs each index of A[]? (A should be an array of Point structs).
No, there's no necessary to write a for loop. The malloc function will do exactly what you want.

Answer 2

Is sum in the c++ code the c++ sum function, or is it a Point struct?
In your case, it is a Point struct.
Point *A = new Point[N], sum;
is equivalent to:
Point *A = new Point[N];
Point sum; //I have no idea why naming is sum
If you need Point* for sum, you should write it in the following way:
Point *A = new Point[N], *sum;
For allocating the memory in C, I don't think my method works
It does not work, syntax is wrong. Try:
EDIT: thanks to #mch, you should not use cast for malloc.
typedef struct Point Point;
Point* A = malloc(N * sizeof(Point));