C

1. Introduction to C

• History of C

The C programming language was developed in the early 1970s by Dennis Ritchie at Bell Labs. It was designed as a system programming language to write operating systems, specifically UNIX. The language evolved from two previous languages, B and BCPL (Basic Combined Programming Language). C quickly became popular due to its efficiency and control, allowing programmers to write system-level code with high performance.

• Features of C

C is a general-purpose, procedural language that provides a wide range of features:

• Portability: C programs can run on various types of computer systems with minimal or no modification.

• Low-level Access: C provides low-level access to memory through pointers, which is essential for system programming.

• Structured Language: C allows complex programs to be broken into simpler sub-programs (functions).

• Rich Library: C comes with a standard library that provides numerous built-in functions for tasks like input/output, string handling, mathematical computations, etc.

• Efficiency: C is highly efficient, making it suitable for developing operating systems, compilers, and embedded systems.

• Modularity: Code can be separated into multiple files, allowing better organization and management

• Structure of a C Program

A basic C program consists of one or more functions, the most important of which is the main() function. This function serves as the entry point of the program. Here's a simple structure of a C program:

#include <stdio.h> // Preprocessor directive to include standard I/O library

// Function prototype declarations
void function1();
void function2();

int main() {
    // Code to be executed
    printf("Hello, World!\n");
    return 0; // Return statement to end the program
}

// Function definitions
void function1() {
    // Code for function1
}

void function2() {
    // Code for function2
}

• Preprocessor Directives: These begin with a '#' and are processed before compilation. They include header files and define constants or macros.

• Main Function: int main() is where the program execution starts. The return 0; statement indicates successful program termination.

• Function Prototypes and Definitions: Functions can be declared before the main() function and defined after it. This allows the program to use them in a modular way.

• Compiling and Executing a C Program

To run a C program, it needs to be compiled and then executed. Here are the steps involved:

1. Writing the Code: Write the C code in a text editor and save it with a .c extension, for example, hello.c.

2. Compiling the Code: Use a C compiler to convert the source code into an executable file. Common compilers include gcc (GNU Compiler Collection) and clang. For example, using gcc:
   

gcc hello.c -o hello

• This command compiles hello.c and produces an executable named hello.
  

• 3. Running the Executable: Execute the compiled program by typing the name of the executable

./hello

This will run the program and display the output.

Example

Here's an example to illustrate the concepts:

#include <stdio.h>

int main() {
    // This is a comment
    printf("Hello, C Programming!\n"); // Print message to the console
    return 0;
}

• Comments: Lines beginning with // are comments and are ignored by the compiler. They are used to explain the code.

• #include <stdio.h>: This preprocessor directive includes the standard input-output library, which is necessary for using the printf function.

• printf Function: This function prints the specified message to the console.

By following these steps and understanding these concepts, you can write, compile, and execute basic C programs.