Tips and Tricks for C++

Tips and Tricks for C++.md

Tips and Tricks for C++

Arrays and Pointers

int myArray[] = {1,2,3};
int *myPointer = myArray;

// We can change the value of the array's indexes.
// This line change the 2th index of myArray to 5.
*(myArray + 1) = 5;

for(int i = 0; i <= 2; i++) {
cout << i << "\n";

Pointer to Pointers

   int a = 9;
   int *p = &a;
   int **pp = &p;

   // Both has same data.
   cout << *p << "\n";
   cout << **pp << "\n";

   // Basically the releationship is: **pp -> *p -> a=9
   // You can also have 3 leveldeep pointer: ***p, which point to pointer of pointer.

Array of Pointers to Array

   int a[] = {1,2};
   int b[] = {3,4,5};

   // We have an array of pointers which the first index point to `a` array and the seconde index point to `b` array.
   int *p[] = {a,b};

   cout << *(p(1)+2); // 5

Pointers to Multidimensional Array

   int a[2][3] = {1,2,3,4,5,6};
   // Define a Pointer. It's size must be equal to array's column size.
   int (*p)[3]; // It must point to all dimensions except the first one.
   
   int *p[] = {a,b};

   cout << *(*p + 1); // 2, points to the first row.
   cout << *(p(1) + 2); // 5, points to the second row.

Pointers to Functions

   // If we have a function like:
   int fn(int num) {
      return num * num;
   }
   // Then we can also define a pointer like:
   int (*p)(int);
   // It means we have an pointer which accept and `int` parameter and returns `int` value that it can be used 
   // just like functions.

   // Asign the funciton definition to pointer:
   p = fn;
   int k = p(554);

   // When we call the pointer just like the function, it's action like function itself. 

Array of Pointers to Functions

   // If we have theese function prototypes:
   int sum(int, int);
   int prod(int, int);

   // Then we can have arrays of pointers to functions.
   // pass prototypes for array:
   int (*p[2])(int, int) = {sum, prod};

   int val = (*p[0])(2,3);

Pointers to function as parameter of another function

   // If we have theese function prototypes:
   int sum(int, int);
   int prod(int, int);
   int pointerFun(int (*p)(int, int), int, int);

   // We can pass other functions as pointer to `pointerFun()`.
   pointerFun(sum, 2,3);
   pointerFun(prod, 2,3);

Pass Pointers as Arguments to Functions

   // Prototype:
   void f(int *);

   int a = 2;
   f(&a);

   // Prototype implementation:
   void f(int *a) {
      *a = *a+5; // We change the value by reference
   }

Void Pointers

You can use void keyword for pointers declarations to act as ans genenric like variavle:

   int a = 2;
   float b = 2.5;
   void *p;

   *p = &a;
   cout << *(int *)p;

   *p = &b;
   cout << *(int *)p;

   // Error! -> cout << *p;

new & delete

The new keyword assign space to variables in Heap and not the program segment which not freed after end of the program. Make sure to run delete after usage.

   int *a = new int;
   a = 2;
   
   // End of the day:
   delete a;

   // You can specifie the value of the pointer in declaraition:
   int *b = new int(3); // Menas b is 3.

   int *c = new int[2]; // Allocate an array with 2 index.

   delete []c;