References

References are related to pointers - one needs to understand the first one. They work similary like pointers. "References are pointers in disguise." References need to reference an already existing value, therefore they reference a variable.

int a = 5; 
// that's basically it "ref" is also called an alias. 
int& ref = a; 
// we can use ref now as if it were a, for example logging it. 

References can be used to make working with variables across different scopes easier:

void increment(int value) {
  value++; 
}

int main() {
  int a = 5; 
  increment(a); 
  cout << a << endl; 
  // prints 5
}

The shown code will simply copy the value of a into the scope of "increment". Therefore, within the functions scope a brand new variable with the value of 5 will be created, and then incremented. a in the original scope of the main function is not changed.

Instead, we can pass it as a reference in order to increment the original variable:

void increment(int& value) {
  value++; 
}

int main() {
  int a = 5; 
  increment(a); 
  cout << a << endl; 
  // prints 6
}

This does the same as the following code, but in an easier manner

void increment(int* value) {
  (*value)++; 
}

int main() {
  int a = 5; 
  increment(&a); 
}