C++ Variables, constants, and expressions

Variables and constants are used to store values in C++ programs, and expressions are used to combine and manipulate these values. Here's a brief overview of each:

Variables:

  • Variables are used to store values that can change during the execution of a program.
  • To declare a variable, you specify its data type and name, like this: int age; or double price;.
  • You can then assign a value to the variable using the assignment operator (=), like this: age = 25; or price = 3.14;.
  • You can also declare and assign a value to a variable in a single statement, like this: int count = 0;.

Constants:

  • Constants are used to store values that cannot be changed during the execution of a program.
  • To declare a constant, you use the const keyword, like this: const int MAX_VALUE = 100; or const double PI = 3.14;.
  • Once a constant is declared and initialized, its value cannot be changed.

Expressions:

  • Expressions are combinations of values, variables, and operators that are used to perform calculations or comparisons.
  • For example, 3 + 4 is an expression that evaluates to the value 7.
  • Expressions can also include variables and constants, like this: age + 1 or PI * radius * radius.
  • C++ supports a wide range of operators for combining values and variables into expressions, including arithmetic operators like +, -, *, and /, as well as comparison operators like ==, !=, <, >, <=, and >=.

Here's an example that combines variables, constants, and expressions in a C++ program:

cpp
#include <iostream> 
using namespace std; 
int main() 
{
const double PI = 3.14; 
int radius = 5; 
double area;

   area = PI * radius * radius; 
 cout << "The area of a circle with radius " << radius << " is " << area << endl;

   return 0;
}

This program declares a constant PI and a variable radius, and then uses these values to calculate the area of a circle using the expression PI * radius * radius. The cout statement is used to print the result to the console.

 

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