Essential C++ # 01. Basic C++ Programming

Chapter 1. Basic C++ Programming

📌Composition of a C++ Class

• A header file that provides a declaration of the operation supported by the class
• A program text file that contains the implementation of those operations

📌Common Initialization Syntax VS Constructor Syntax

• common:

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int number = 0;

• constructor syntax:

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int number(10);

📌Constructor Syntax

The reason behind this syntax refers to multiple parameter initialization.(very common in Class)

But the primitive type can also be initialized like so.

📌Initialize an array

1️⃣:

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int seq_size = 6;
int elem_seq[seq_size] = {
    1, 2, 3,
    4, 5, 6
};

2️⃣:

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int elem_seq[] = {
  1, 2, 3,
  4, 5, 6
};

📌Initialize a vector

1️⃣:

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int seq_size = 3;
vector<int> elem_seq(seq_size);
elem_seq[0] = 1;
elem_seq[1] = 2;
elem_seq[2] = 3;

2️⃣:

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int seq_size = 3;
int elem_val[seq_size] = {1, 2, 3};
vector<int> elem_seq(elem_val, elem_val + seq_size);

elem_val is actually the address passed in the vector. The + seq_size indicates how long the array should be.

📌Why pointer?

A pointer introduces a level of indirection to a program. Rather than manipulate an object directly😑, we manipulate a pointer that holds the address of an object😍.

📌How to use a pointer?

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int ival = 1024;
int* pi;             // pi is a pointer to an object of type int
&ival;               // evaluates to the address of ival by using `&`
pi = &ival;          // pass the address of ival to pi

📌Different Style of Pointer

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int* pi = &ival;
int *pi = &ival;

The preceding are both correct. If you prefer the first one, please take into account the following:

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int* pi, pi2;

pi is a pointer, pi2 is just an integer. If you want both of them are pointer, you should:

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int* pi, * pi2;

📌Dereference a pointer

You can take the value of the pointer points to by using *.

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if (*pi != 1024)
{
    *pi = 1024;
}

📌Be patient when you are learning pointer

The initial complexity of using a pointer comes from its confusing syntax.🤣

📌Caution using pointer!⚠

A pointer can possibly points to no object!

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// initialize a pointer to address no object
int *pi = 0;

Therefore, to guard against dereferencing a null pointer, we must assure if its address value is zero before using...

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// safe check
if (pi && *pi!=1024)
{
    *pi = 1024;
}

The if (pi && ...) assure the pointer pi is not empty.

📌Complex Example of Pointers

We have 6 vector sequence objects:

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vector<int> fibonacci, lucas, pell, triangular, square, pentagonal;

Suppose we have a pointer points to fibonacci:

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vector<int> *fib_ptr = &fibonacci;

Or more than that, an array of pointers whose type is vector<int>*...

vector<int>* ptrs[6] = {
    &fibonacci, &lucas, &pell, &triangular, &square, &pentagonal
};

📌Function using ->() and .()

In C#, a function can be called like this:

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number.ToString();

But in C++, you may see 2 ways of invoking a function:

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xxx.DoSomething();
xxx->DoSomething();

The difference is that:

When xxx is an object of a class, it uses xxx.Function();

When xxx is a pointer to an object, it uses xxx->Function();