Added Day 4 Content (#73)

* Update constants-in-cpp.md

* Update constants-in-cpp.md

docs/day-04/constants-in-cpp.md

@@ -6,15 +6,84 @@ sidebar_label: "Constants"
 slug: constants-in-cpp
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-TASK:
+## What is Constants in C++?
+Constants in C++ are fixed values that cannot be altered during the execution of a program. They are used to define values that should remain unchanged throughout the program, providing a way to ensure data integrity and improving code readability.
+
 
-1. What is Constants in C++?
-2. How to Declare Constants in C++?
-3. How to Define Constants in C++?
-4. How to Use Constants in C++?
-5. What are the Advantages of Constants in C++?
-6. Best Practices for Using Constants in C++.
-7. Examples of Constants in C++.
 
 IMAGE FILE:
-![Constants in CPP](../../static/img/day-04/constants-in-cpp.png)
+![Constants in CPP](../../static/img/day-04/constants-in-cpp.png)
+
+## How to Declare Constants in C++?
+Constants can be declared in C++ using the `const` keyword. The `const` keyword is placed before the data type of the variable to indicate that its value will not change.
+
+### Example:
+```cpp
+const int DAYS_IN_WEEK = 7;
+const float PI = 3.14159;
+```
+
+## How to Define Constants in C++?
+Constants are defined at the time of declaration by assigning them a fixed value. Once defined, their value cannot be modified.
+
+### Example:
+```cpp
+const double GRAVITY = 9.81; // gravitational constant in m/s^2
+const char NEWLINE = '\n'; // newline character
+```
+
+## How to Use Constants in C++?
+Constants are used just like regular variables in expressions, function calls, and other places where a variable would be used. The key difference is that their value remains unchanged.
+
+### Example
+
+```cpp
+const int MAX_USERS = 100;
+
+int main() {
+    int users = MAX_USERS;
+    std::cout << "Maximum number of users: " << users << std::endl;
+    return 0;
+}
+```
+
+## What are the Advantages of Constants in C++?
+- Readability: Constants make the code more readable by giving meaningful names to fixed values.
+- Maintainability: Constants allow easy modification of values without changing multiple instances in the code.
+- Safety: Constants prevent accidental modification of values that should remain fixed, reducing bugs and errors.
+- Optimization: Constants can sometimes allow the compiler to optimize the code better since their values are known at compile time.
+
+## Best Practices for Using Constants in C++:
+- Use Descriptive Names: Choose names that clearly describe the value or purpose of the constant.
+- All Uppercase with Underscores: Use all uppercase letters with underscores to separate words for naming constants, making them easily distinguishable from variables.
+- Define Constants at the Top: Define all constants at the beginning of the file or in a dedicated section for easy reference and modification.
+- Group Related Constants: Group related constants together to improve code organization.
+- Use constexpr for Compile-Time Constants: Use constexpr when the constant value can be determined at compile time for better performance.
+
+### Example:
+```cpp
+constexpr int ARRAY_SIZE = 50;
+const double SPEED_OF_LIGHT = 299792458.0; // in meters per second
+```
+
+## Examples of Constants in C++
+
+```cpp
+#include <iostream>
+
+const int MAX_AGE = 120;
+constexpr double PLANCK_CONSTANT = 6.62607015e-34;
+
+int main() {
+    const char GRADE = 'A';
+    const std::string SCHOOL_NAME = "Greenwood High";
+
+    std::cout << "Max age allowed: " << MAX_AGE << std::endl;
+    std::cout << "Planck constant: " << PLANCK_CONSTANT << std::endl;
+    std::cout << "Grade: " << GRADE << std::endl;
+    std::cout << "School name: " << SCHOOL_NAME << std::endl;
+
+    return 0;
+}
+```
+