How to create an input method in C++ with pointers

Question

I want to create an input method that creates two ints with Pointers. It would be nice if you could help me or give me any tips. :)

my method:

void inputTest(int* x, int* y) {
    cin >> x;
    cin >> y;
}

my main:

int *x = 0;
int *y = 0;
cout << "Input: " << endl;


//set input from user x,y with input method 
inputTest(x,y);

Answer 1

First of all, you want to read ints, not int*s, so you need to dereference the pointers:

void inputTest(int* x, int* y) {
    cin >> *x;
    cin >> *y;
}

Then you need to pass valid pointers to the function - yours are null pointers and point nowhere at all.
The best way to do this is to first create two ints and then acquire their locations with the "address-of" operator, &.

int x = 0;
int y = 0;
cout << "Input: " << endl;
inputTest(&x, &y);

Answer 2

I'm new to pointers so I want to try it that way.. :)

Ok, then first lesson: Do not use pointers when you don't have to. Pointers can cause the most nasty bugs that you dont get without them.

Next: Pointers are just pointers. The can point to something. A int* can point to an int. Your pointers do not point to anything meaningful.

To store integer values you need ints somewhere. Having pointers pointing somewhere is not sufficient. Once you have a int, eg int x; then &x will give you a int* namely the address of x (& is called the address-of operator, but dont get confused, & can have a different meaning, see below). If you have the pointer, int* p = &x; then you can dereference the pointer to get back x: *p = 5; will set the value of x to 5. Using that you could write

void inputTest(int* x, int* y) {
    std::cin >> *x;    
    std::cin >> *y;
}
int main() {
   int x,y;
   inputTest(&x,&y);
   std::cout << x << " " << y;
}

BUT (would like to make it even more bold, because it really is a big "but"). There is an alternative and this is what you should use here. Pointers as parameters are useful when "not pointing anywhere" is an allowed parameter. For a fucntion that wants to read input from user and store that somewhere an invalid pointer is of little use. Better is to disallow such invalid input and use references:

void inputTest(int& x, int& y) {
    std::cin >> x;    
    std::cin >> y;
}
int main() {
   int x,y;
   inputTest(x,y);
   std::cout << x << " " << y;
}

I feel a bit bad for writing this answer, because when you are completely new to pointers, reading an answer here will not be enough to get a proper understanding. Get a book and read it.

Answer 3

You need to dereference the pointer in order to assign a value to the pointed location in memory.

void inputTest(int* xptr, int* yptr) {
    cin >> *xptr;
    cin >> *yptr;
}

int* x = 0 creates a pointer to location 0 in memory. Instead, we want to allocate memory, and then point to that memory. We can initialize x as int x = 0 and then get a pointer to it by using &x.

int x = 0;
int y = 0;
cout << "Input: " << endl;
inputTest(&x,&y);

You can also use references...

void inputTest(int& x, int& y) {
    cin >> x;
    cin >> y;
}

int x = 0;
int y = 0;
cout << "Input: " << endl;
inputTest(x,y);