Konstantalar

Konstanta nima?

Konstanta — bu qiymat berilgandan keyin o‘zgartirib bo‘lmaydigan qiymat.

Konstantalar dastur ishlayotgan vaqtda o‘zgarmay qolishi kerak bo‘lgan qiymat uchun foydali: masalan, PI qiymati, haftadagi kunlar soni yoki o‘zgarmas URL.

Yangilanishi mumkin bo‘lgan o‘zgaruvchilardan farqli ravishda, konstantalar yaratilgandan keyin bir xil qiymatni saqlab qoladi:

PI = 3.14159
print(PI)

const PI = 3.14159;
console.log(PI);

final double PI = 3.14159;
System.out.println(PI);

const double PI = 3.14159;
cout << PI;

Nima uchun konstantalardan foydalanish kerak?

Konstantalardan foydalanish kodingizni tushunish va qo‘llab-quvvatlashni osonlashtiradi:

• O‘qilishi oson: PI yoki DAYS_IN_WEEK kabi nomlar son nimani anglatishini tushuntirib beradi.
• Xavfsizlik: Konstantalar muhim qiymatlarni tasodifan o‘zgartirilishdan himoya qiladi.
• Oson yangilash: Agar konstantani (masalan, soliq stavkasini) o‘zgartirish kerak bo‘lsa, uni faqat bir joyda yangilaysiz.

Konstantani o‘zgartirish

Konstantaga qiymat berilgandan keyin uni o‘zgartirishga urinish, tilga qarab, odatda xatoga olib keladi yoki e’tiborsiz qoldiriladi.

PI = 3.14159
PI = 3   # This works in Python, but it is not recommended
print(PI)

const PI = 3.14159;
PI = 3;   // Error: Assignment to constant variable

final double PI = 3.14159;
PI = 3;   // Error: cannot assign a value to final variable

const double PI = 3.14159;
PI = 3;   // Error: assignment of read-only variable

Konstantalar amalda

Mana konstantalarning keng tarqalgan bir nechta misoli:

• PI = 3.14159 (pi matematik konstantasi)
• DAYS_IN_WEEK = 7
• URL = "https://example.com"

DAYS_IN_WEEK = 7
print("A week has", DAYS_IN_WEEK, "days")

const DAYS_IN_WEEK = 7;
console.log("A week has " + DAYS_IN_WEEK + " days");

final int DAYS_IN_WEEK = 7;
System.out.println("A week has " + DAYS_IN_WEEK + " days");

const int DAYS_IN_WEEK = 7;
cout << "A week has " << DAYS_IN_WEEK << " days";