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C++ Cookbook

Table of Contents

  1. Fundamental
  2. Data Types
  3. Decision Making
  4. Loops
  5. Arrays
  6. Strings

Fundamental

Variables

วิธีการสร้างตัวแปร จะอยู่ในรูปแบบของ VAR_TYPE VAR_NAME = VALUE; เช่น

#include <iostream>

int main()
{
    int money = 100;
    double height = 160.5;

    return 0;
}

หรือเราจะไม่กำหนดค่าเริ่มต้นให้กับตัวแปรก็ได้ แต่ compiler ทำการสุ่มค่าให้

#include <iostream>
using namespace std;

int main()
{
    int money;
    cout << money; // money = some random number

    return 0;
}

Program Example : สลับค่าตัวแปร

#include <iostream>
using namespace std;

int main()
{
    int a = 10;
    int b = 20;

    int temp = a;
    a = b;
    b = temp;

    cout << a << " " << b;

    return 0;
}
#include <iostream>
using namespace std;

int main()
{
    int a = 10;
    int b = 20;

    a = a + b; // Step 1: Add both numbers
    b = a - b; // Step 2: Subtract the new value of a by b to get original a
    a = a - b; // Step 3: Subtract the new value of b from the new value of a to get original b

    cout << a << " " << b;

    return 0;
}

Constants

วิธีการสร้างค่าคงที่ด้วยคำสั่ง const เพื่อป้องกันไม่ให้ตัวแปรถูกเปลี่ยนแปลงค่า

#include <iostream>

int main()
{
    const int number = 999;
    number = 199; // can't update value

    return 0;
}

Naming conventions

ในภาษา C++ มักจะใช้ Camel Case กัน

#include <iostream>

int main()
{
    int item_count; // Snake Case
    int ItemCount;  // Pascal Case
    int itemCount;  // Camel Case

    return 0;
}

Mathematical expressions

#include <iostream>

int main()
{
    int x = 10;
    int y = 3;
    int z;

    z = x + y;
    z = x - y;
    z = x * y;
    z = x / y;
    z = x % y;

    x += 1;

    x++;
    ++x;

    z = x++;
    z = ++x;

    return 0;
}

Order of Operation

#include <iostream>

int main()
{
    // ()
    // * and /
    // + and -
    double x = (1 + 2) * 3;

    return 0;
}

Writing output to the console

เขียนข้อมูลไปที่ console

#include <iostream>
using namespace std;

int main()
{
    int x = 10;
    cout << "x = ";
    cout << x;

    return 0;
}

สามารถรวบให้เหลือในบรรทัดเดียวได้

#include <iostream>
using namespace std;

int main()
{
    int x = 10;
    cout << "x = " << x;

    return 0;
}

ใช้คำสั่ง endl (end line) เพื่อขึ้นบรรทัดใหม่ได้

#include <iostream>
using namespace std;

int main()
{
    int x = 10;
    int y = 20;
    cout << "x = " << x << endl;
    cout << "y = " << y;

    return 0;
}

สามารถรวบคำสั่งได้ (แนะนำให้ tab บรรทัดที่ 2 ขึ้นไปให้ตำแหน่งอยู่ตรงกับผลลัพธ์)

#include <iostream>
using namespace std;

int main()
{
    int x = 10;
    int y = 20;
    cout << "x = " << x << endl
         << "y = " << y;

    return 0;
}

Program Example : โปรแกรมคำนวน vat 7% + service charge 10%

#include <iostream>
using namespace std;

int main()
{
    double price = 5000;
    cout << "Price: ฿" << price << endl;

    const double tax = .07;
    double stateTax = price * tax;
    cout << "State Tax: ฿" << stateTax << endl;

    const double serviceCharge = .1;
    double stateServiceCharge = price * serviceCharge;
    cout << "State Service Charge: ฿" << stateServiceCharge << endl;

    double totalTax = stateTax + stateServiceCharge;
    cout << "Total Tax: ฿" << totalTax;

    return 0;
}

Reading input from the console

อ่านค่าจาก console ด้วยคำสั่ง cin

#include <iostream>
using namespace std;

int main()
{
    cout << "Enter a value: ";

    int value;
    cin >> value;

    cout << value;

    return 0;
}

ในการรับค่าตัวแปรมากกว่า 1 ตัวสามารถใช้คั่นด้วย space หรือ enter ก็ได้

#include <iostream>
using namespace std;

int main()
{
    cout << "Enter values for x and y: ";

    int x;
    int y;
    cin >> x;
    cin >> y;

    cout << x + y;

    return 0;
}

เช่นเดียวกับการใช้งาน cout เราสามารถรวบคำสั่ง cin ได้

#include <iostream>
using namespace std;

int main()
{
    cout << "Enter values for x and y: ";

    int x;
    int y;
    cin >> x >> y;

    cout << x + y;

    return 0;
}

Program Exmaple : Fahrenheit to Celsius

#include <iostream>
using namespace std;

int main()
{
    cout << "Fahrenheit: ";
    int fahrenheit;
    cin >> fahrenheit;

    double celsius = (fahrenheit - 32) / 1.8;
    cout << celsius;

    return 0;
}

Cmath library

document : https://cplusplus.com/reference/cmath/

ตัวอย่างการใช้งานฟังก์ชันจาก cmath library

#include <iostream>
#include <cmath>
using namespace std;

int main()
{
    int p = pow(2, 5);
    cout << "Power = " << p << endl;    // ยกกำลัง

    double c = ceil(1.34);
    cout << "Ceil = " << c << endl;     // ปัดขึ้น

    double f = floor(1.74);
    cout << "Floor = " << f;            // ปัดลง
    return 0;
}

Program Example - คำนวณพื้นที่วงกลม

#include <iostream>
#include <cmath>
using namespace std;

int main()
{
    cout << "Enter radius: ";
    double radius;
    cin >> radius;

    const double pi = 3.14;
    double area = pi * pow(radius, 2);

    cout << area;
    return 0;
}

Comments

การคอมเมนต์โค้ด เพื่อผู้อื่น และตัวเองในอนาคต

#include <iostream>

int main()
{
    // Hello World
    // This is a comment

    /*
     Hello World
     This is also a comment
     */

    return 0;
}

Data Types

Fundamental Types

Integer Number

Type Range
short -32,768 to 32767
int -2,147,483,648 to 2,147,483,647
long -2,147,483,648 to 2,147,483,647
long long -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807

Floating-point Number

Type Range Precision (Digits)
float -3.4E38 to 3.4E38 7
double -1.7E308 to 1.7E308 15
long double -3.4E932 to 1.7E4832

Others Types

Type Range
bool true / false
char 1 character

Initializing Variables

#include <iostream>

int main()
{
    double price = 25.50;
    float taxRate = 0.07f;
    long money = 90000L;
    long long lifePoint = 999999999LL;
    char letter = 'a';
    bool isValid = false;

    return 0;
}

Formatting Output

Format floating-point number

#include <iostream>
#include <iomanip>
using namespace std;

int main()
{
    cout << fixed << setprecision(2) << 124.45678;

    return 0;
}

Data Limits

#include <iostream>
using namespace std;

int main()
{
    cout << numeric_limits<int>::min() << endl  // min = -2,147,483,648
         << numeric_limits<int>::max();         // max =  2,147,483,647

    return 0;
}

Type Casting

#include <iostream>
using namespace std;

int main()
{
    int x = 10;
    int y = 3;

    double z = (double)x / y; // Cast variable x from INT to DOUBLE
    cout << z;

    return 0;
}

Working with Booleans

#include <iostream>
using namespace std;

int main()
{
    bool result = false;
    cout << result;              // 0
    cout << boolalpha << result; // false

    bool result2 = true;
    cout << result2;              // 1
    cout << boolalpha << reslut2; // true

    return 0;
}

Decision Making

Comparison Operators

Operator Name Example
> Grater than x > y
< Less than x < y
>= Grather than or equal to x >= y
<= Less than or equal to x <= y
== Equal to x == y
!= Not equal x != y 
#include <iostream>

int main()
{
    int x = 10;
    int y = 20;

    bool result = x > y;    // result = false
    bool result2 = x == 10; // result2 = true

    return 0;
}

Logical Operators

Operator Name Example
&& Logical and x > 5 && x < 10
|| Logical or x < 0 || x > 1
! Logical not !(x >= 2 && x <= 7) 
#include <iostream>

int main()
{
    int age = 2;

    bool isBaby = age >= 1 && age <= 3;      // isBaby = true
    bool isNotBaby = !(age >= 1 && age <= 3) // isNotBaby = false

    return 0;
}

Order of Logical Operators

#include <iostream>

int main ()
{
    // ()
    // !
    // &&
    // ||

    bool a = true;
    bool b = false;

    bool result1 = b || !a;     // result1 = false
    bool result2 = a || b && b; // result2 = true

    return 0;
}

IF Statement

if (boolean)
{
    // do statements when boolean == true
}
#include <iostream>
using namespace std;

int main()
{
    int number = 100;
    if (number > 0)
    {
        cout << "Positive Number" << endl;
    }

    cout << "End Program";

    return 0;
}

Program Example : โปรแกรมคำนวณเกรด

#include <iostream>
using namespace std;

int main()
{
    int score = 70;

    if (score >= 80)
    {
        cout << "Grade A";
    }

    if (score >= 70 && score <= 79)
    {
        cout << "Grade B";
    }

    if (score >= 60 && score <= 69)
    {
        cout << "Grade C";
    }

    if (score <= 59)
    {
        cout << "Grade D";
    }

    return 0;
}

IF-ELSE Statement

if (boolean)
{
    // do statements when boolean == true
}
else
{
    // do statements when boolean == false
}
#include <iostream>
using namespace std;

int main()
{
    int number = 100;
    if (number > 0)
    {
        cout << "Positive Number" << endl;
    }
    else
    {
        cout << "Not a Positive Number" << endl;
    }

    cout << "End Program";

    return 0;
}

Program Example : โปรแกรมคำนวณเกรด

#include <iostream>
using namespace std;

int main()
{
    int score = 70;
    if (score >= 80)
    {
        cout << "Grade A";
    }
    else
    {
        if (score >= 70)
        {
            cout << "Grade B";
        }
        else
        {
            if (score >= 60)
            {
                cout << "Grade C";
            }
            else
            {
                cout << "Grade D";
            }
        }
    }

    return 0;
}

แต่เนื่องจากในแต่ละ statement มีเพียง 1 คำสั่ง สามารถละเว้น {} ได้ เพื่อให้โค้ดอ่านง่ายขึ้น

#include <iostream>
using namespace std;

int main()
{
    int score = 70;
    if (score >= 80)
        cout << "Grade A";
    else if (score >= 70)
        cout << "Grade B";
    else if (score >= 60)
        cout << "Grade C";
    else
        cout << "Grade D";

    return 0;
}

Conditional Operator

#include <iostream>

int main()
{
    int price = 1000;

    // double tax;
    // if (price >= 1000)
    // {
    //     tax = .07;
    // }
    // else
    // {
    //     tax = .1;
    // }
    double tax = (price >= 1000) ? .07 : .1;

    return 0;
}

Program Example : ค้นหาจำนวนที่มากกว่า จากข้อมูลเข้าสองจำนวน

#include <iostream>
using namespace std;

int main()
{
    int first;
    int second;
    cin >> first >> second;

    int result;
    if (first > second)
        result = first;
    else
        result = second;

    cout << result;

    return 0;
}
#include <iostream>
using namespace std;

int main()
{
    int first;
    int second;
    cin >> first >> second;

    int result = (first > second) ? first : second;

    cout << result;

    return 0;
}

Loops

For Lops

for (initialization; condition; update)
{
    // do staetment if condition is true
}
#include <iostream>
using namespace std;

int main()
{
    for (int i = 0; i < 5; i++)
    {
        cout << "Hello World " << i << endl;
    }

    for (int i = 10; i >= 6; i--)
    {
        cout << "Hello World " << i << endl;
    }

    for (int i = 1; i <= 10; i++)
    {
        if (i % 2 == 0)
        {
            cout << i << endl;
        }
    }

    for (int i = 1; i <= 10; i += 2)
    {
        cout << i << endl;
    }

    return 0;
}

Program Example : หาผลรวมตัวเลขสิบตัวจาก input

#include <iostream>
using namespace std;

int main()
{
    int number;
    int sum = 0;

    for (int i = 0; i < 10; i++)
    {
        cin >> number;
        sum += number;
    }

    cout << sum;
}

Range-based for Loops

int numbers[5] = { 10, 20, 30, 40, 50 }

for (int number: numbers)
    cout << number << endl;

for (auto number: numbers)
    cout << number << endl;

While Loops

while (condition)
{
    // Do statement if condition is True
}
#include <iostream>
using namespace std;

int main()
{
    int i = 0;
    while (i < 5)
    {
        cout << "Hello World " << i << endl;
        i++;
    }

    return 0;
}
#include <iostream>
using namespace std;

int main()
{
    int number = -1;

    while (number != 0)
    {
        cin >> number;
    }

    return 0;
}

Do-while Loops

do
{
    // Always execute at least 1 time.
    // Do statement until condition is false.
} while (condition);
#include <iostream>
using namespace std;

int main()
{
    int number;

    do
    {
        cin >> number;
    } while (number != 0);

    return 0;
}

Break and continue statements

break; used to jump out of a loop.

for (int i = 0; i < 10; i++) {
  if (i == 5)
    break;

  cout << i << endl;
}

continue used to continues with the next iteration in the loop.

for (int i = 0; i < 10; i++) {
  if (i == 5)
    continue;

  cout << i << endl;
}

Arrays

Creating Arrays

int numbers[5]; // We got numbers[0], numbers[1], ..., numbers[4]
numbers[0] = 10;
numbers[1] = 20;
numbers[2] = 30;
numbers[3] = 40;
numbers[4] = 50;

cout << numbers[0] << endl
     << numbers[1] << endl
     << numbers[2] << endl
     << numbers[3] << endl
     << numbers[4] << endl:
int numbers[5] = {10, 20, 30, 40, 50};
int numbers[5];
cin >> numbers[0]
    >> numbers[1]
    >> numbers[2]
    >> numbers[3]
    >> numbers[4];

cout << numbers[0] << endl
     << numbers[1] << endl
     << numbers[2] << endl
     << numbers[3] << endl
     << numbers[4] << endl:
#include <iostream>
using namespace std;

int main()
{
    int n;
    cin >> n;

    int numbers[n];
    for (int i = 0; i < n; i++)
        cin >> numbers[i];

    for (int i = 0; i < n; i++)
        cout << numbers[i] << " ";

    // Or use Ranged-based for loop
    // for (int number: numbers)
        // cout << number << " ";
}

Copying Arrays

int first[3] = {10, 20, 30};
int second[3];

for (int i = 0; i < 3; i++) // ! Can't use Ranged-based for loop !
    second[i] = first[i];

for (int number: second)
    cout << number << " ";

Comparing Arrays

int first[] = {10, 20, 30};
int second[] = {10, 20, 30};

bool isEqual = true;
for (int i = 0; i < 3; i++)
{
    if (first[i] != second[i])
    {
        isEqual = false;
        break;
    }
}

cout << boolalpha << isEqual;

Upacking Arrays (Structured Binding)

int numbers[3] = {10, 20, 30};

// int x = numbers[0];
// int y = numbers[1];
// int z = numbers[2];
auto [x, y, z] = numbers;

Sorting Arrays

int numbers[5] = {50, 10, 40, 20, 30};

// Bubble sort - Asecdenting order
for (int i = 0; i < 4; i++)
{
    for (int j = 0; j < 4; j++)
    {
        if (numbers[j] > numbers[j + 1])
        {
            int temp = numbers[j];
            numbers[j] = numbers[j + 1];
            numbers[j + 1] = temp;
        }
    }
}

for (int number: numbers)
    cout << number << " ";

Strings

String fundamental

#include <iostream>
using namespace std;

int main()
{
    string message = "Hello"; // Define string

    cout << message[0] << endl; // Accessing char in string

    message[0] = 'h'; // Updating value in string
    cout << message << endl; // hello

    cout << message.length() << endl; // 5

    message += " World";
    cout << message << endl; // Hello World

    string anotherMessage = message;
    if (message == anotherMessage) // Compare 2 strings
        cout << "Same";

    cout << boolalpha << message.empty(); // false


    return 0;
}

String use cases

string message = "Hello World";
for (int i = 0; i < message.length(); i++)
{
    if ('a' <= message[i] and message[i] <= 'z')
        cout << message[i] << endl;
}
string message = "Hello World";
int countUpperCase = 0;

for (int i = 0; i < message.length(); i++)
{
    if ('A' <= message[i] and message[i] <= 'Z')
        countUpperCase += 1;
}

cout << "countUppercase = " << countUpperCase;
string message = "Hello World";
int countAlphabet = 0;

for (int i = 0; i < message.length(); i++)
{
    bool isUpperCase = 'A' <= message[i] and message[i] <= 'Z';
    bool isLowerCase = 'a' <= message[i] and message[i] <= 'z';

    if (isUpperCase || isLowerCase)
        countAlphabet += 1;
}

cout << "countAlphabet = " << countAlphabet;
string message = "Hello World";

for (int i = 0; i < message.length(); i++)
{
    if ('A' <= message[i] and message[i] <= 'Z')
    {
        message[i] = message[i] + ('a' - 'A');
    }
    else if ('a' <= message[i] and message[i] <= 'z')
    {
        message[i] = message[i] - ('a' - 'A');
    }
}
int letter = 'A';

cout << letter; // 65

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