Variables, data types, and constants

In C, variables, data types, and constants are essential components used to store and manage data. Here’s a code example that demonstrates these concepts:

#include <stdio.h>

#define PI 3.14159  // Constant defined with #define preprocessor

int main() {
    int age = 25;                // Integer variable
    float height = 5.9;          // Floating-point variable
    char initial = 'J';          // Character variable
    const int daysInWeek = 7;    // Constant integer variable

    printf("Age: %d\n", age);
    printf("Height: %.1f\n", height);
    printf("Initial: %c\n", initial);
    printf("Days in a week: %d\n", daysInWeek);
    printf("Value of PI: %.5f\n", PI);

    return 0;
}

Explanation of Variables, Data Types, and Constants

1. Variables

• A variable is a named memory location that can store a value. Each variable has a specific data type that determines what kind of data it can hold, such as integers, floating-point numbers, or characters.
• In this example:
  • int age = 25; declares an integer variable age and assigns it the value 25.
  • float height = 5.9; declares a floating-point variable height to store decimal numbers, assigning it 5.9.
  • char initial = 'J'; declares a character variable initial that stores the character J.

2. Data Types

• int: Used for whole numbers (both positive and negative) without a fractional component. E.g., int age.
• float: Used for single-precision floating-point numbers, allowing for decimal values. E.g., float height.
• char: Used for single characters. It can hold one character enclosed in single quotes, e.g., char initial.

3. Constants

• Constants are values that do not change throughout the program. In C, constants can be defined using the const keyword or with #define directives.
• Using const: const int daysInWeek = 7; defines a constant integer, daysInWeek, that cannot be modified after being assigned 7.
• Using #define: #define PI 3.14159 defines PI as a symbolic constant with the value 3.14159. The preprocessor replaces all occurrences of PI with 3.14159 before compilation.

4. Printing Variables and Constants

• printf("Age: %d\n", age); prints the integer value of age using %d.
• printf("Height: %.1f\n", height); prints the floating-point value of height using %.1f to show one decimal place.
• printf("Initial: %c\n", initial); prints the character stored in initial using %c.
• printf("Days in a week: %d\n", daysInWeek); and printf("Value of PI: %.5f\n", PI); print the values of daysInWeek and PI.

Summary

• Variables store data that can be modified, each with a specific data type.
• Data types specify the kind of data that a variable can hold.
• Constants represent fixed values that do not change throughout the program, either through const or #define.

This basic example highlights these essential building blocks for managing data in a C program.