C Programming Libraries and Constants

C Library

• C libraries are collections of functions and symbols that a program can access.
• Libraries offer several operations that programs can use.
• The standard header file for a C library ends with ".h".
• To open a predefined library, use angle brackets (<>).
• To open a user-defined library, use double quotes ("").

#include Directive

• Gives a program access to a library.
• Tells the preprocessor to insert definitions from a standard header file into the program.
• The preprocessor modifies the code before compilation.
• It also informs the preprocessor about names used in the program that are found in the standard header file.

C Constants

• These fixed values remain unchanged during program execution.
• Types of constants:
  • Character constants: Enclosed in single quotes (e.g., 'A', '+').
  • Integer constants: Whole numbers without fractional components (e.g., 5, -160).
  • Floating constants: Numbers with decimal points followed by fractional components (e.g., 16.234).
  • String constants: Sets of characters enclosed in double quotes (e.g., "bag", "this is good").
  • Backslash character constants: Single-quoted character constants, used for characters that require special handling (e.g., 't' for tab).

CONSTANTS

• Constants are data values that cannot be modified during a program's execution.
• Constants have a specific type.
• Two ways to define them:
  • Using the preprocessor (#define): A global declaration used to assign macro constant values.
  • Using the const keyword: A local declaration, usually within a function.

#define

• Allows text substitution within a program before compilation.
• Identifiers intended for preprocessor replacement are conventionally written in uppercase letters.

Using #define

• Multiple data types can be defined using #define:
  • #define SCORE 100 (integer)
  • #define PI 3.14159 (float)
  • #define code ‘A’ (character)
  • #define MSSG “Hello” (string)

Using the const keyword

• Declare constants within a function.
• Examples:
  • const char MSSG = “Hello”; (character)
  • const float PI = 3.1459; (float)
  • const int year = 2024; (integer)
  • const code = ‘X’; (character)

General Structure of a C Program

• Each C program consists of two sections:
  • Heading section: Includes preprocessor directives, which typically start with #.
  • Executable section: Contains the program's logic, written as code enclosed in curly braces.
• Common elements:
  • #include <stdio.h>: Includes the standard input-output library, essential for functions like printf and scanf.
  • int main(void): The main function, the starting point of every C program.
  • return 0;: Indicates successful execution of the program.
  • Comments: Explanatory text that is ignored by the compiler (often using // or /* ... */).

Sample C Program

• Contains the #include <stdio.h> directive for using input-output operations.
• Demonstrates the int main() function.
• Includes a placeholder printf... for potential code within the function.

This quiz covers important concepts regarding C libraries, including the use of the #include directive and different types of constants in C programming. Test your understanding of how libraries function and the significance of constants in code execution.