C Programming

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Overview of C Programming

C is a high-level and general-purpose programming language that is widely used for system and application software. It provides low-level access to memory and system resources, making it ideal for developing operating systems, embedded systems, and performance-critical applications.

Basic Syntax and Structure

• Comments :
  • Single-line comments start with double slashes (//).

  // This is a single-line comment

  • Multi-line comments are enclosed in /* and */.

  /* 
  This is a multi-line comment 
  spanning multiple lines 
  */

• Preprocessor Directives :
  • Preprocessor directives begin with a hash (#).

  #include 
  #define PI 3.14

• Main Function :
  • The entry point of a C program is the main function.

  int main() {
   printf("Hello, World!");
   return 0;
  }

• Data Types :
  • Common data types include int, float, double, and char.

  int age = 25;
  float height = 5.9;
  double pi = 3.14159;
  char initial = 'A';

Control Structures

• Conditional Statements :
  • if, else if, and else are used for decision making.

  if (age > 18) {
   printf("Adult");
  } else {
   printf("Minor");
  }

• Switch Statement :
  • Used for multi-way branching.

  switch (initial) {
   case 'A':
   printf("Grade A");
   break;
   case 'B':
   printf("Grade B");
   break;
   default:
   printf("Other Grade");
  }

• Loops :
  • for, while, and do-while loops for iteration.

  for (int i = 0; i < 5; i++) {
   printf("%d ", i);
  }
  int j = 0;
  while (j < 5) {
   printf("%d ", j);
   j++;
  }
  int k = 0;
  do {
   printf("%d ", k);
   k++;
  } while (k < 5);

Functions

• Defining Functions :
  • Functions are defined using the return type, function name, and parameters.

  int add(int a, int b) {
   return a + b;
  }
  int main() {
   int sum = add(5, 3);
   printf("Sum: %d", sum);
   return 0;
  }

• Void Functions :
  • Functions that do not return a value.

  void greet() {
   printf("Hello, World!");
  }
  int main() {
   greet();
   return 0;
  }

Arrays and Pointers

• Arrays :
  • Collections of elements of the same type.

  int numbers[5] = {1, 2, 3, 4, 5};
  printf("First element: %d", numbers[0]);

• Pointers :
  • Variables that store memory addresses.

  int x = 10;
  int *ptr = &x;
  printf("Value of x: %d", *ptr); // Output: Value of x: 10

• Pointer Arithmetic :
  • Pointers can be used to navigate arrays and other data structures.

  int arr[3] = {10, 20, 30};
  int *p = arr;
  printf("%d ", *p); // Output: 10
  printf("%d ", *(p + 1)); // Output: 20
  printf("%d ", *(p + 2)); // Output: 30

Structures

• Defining Structures :
  • Structures group variables of different types under a single name.

  struct Person {
   char name[50];
   int age;
  };
  int main() {
   struct Person person1;
   strcpy(person1.name, "Alice");
   person1.age = 30;
   printf("Name: %s, Age: %d", person1.name, person1.age);
   return 0;
  }

File I/O

• Reading from a File :

  FILE *file = fopen("example.txt", "r");
  if (file != NULL) {
   char line[100];
   while (fgets(line, sizeof(line), file)) {
   printf("%s", line);
   }
   fclose(file);
  }

• Writing to a File :

  FILE *file = fopen("example.txt", "w");
  if (file != NULL) {
   fprintf(file, "Hello, World!");
   fclose(file);
  }

Memory Management

• Dynamic Memory Allocation :
  • Memory can be allocated and deallocated using malloc, calloc, realloc, and free.

  int *ptr = (int *)malloc(5 * sizeof(int));
  if (ptr != NULL) {
   for (int i = 0; i < 5; i++) {
   ptr[i] = i + 1;
   }
   free(ptr);
  }

Preprocessor Directives

• Macros :
  • Define constants or functions using the #define directive.

  #define PI 3.14
  #define SQUARE(x) ((x) * (x))
  int main() {
   printf("PI: %f\n", PI);
   printf("Square of 5: %d", SQUARE(5));
   return 0;
  }

• Conditional Compilation :
  • Control the compilation process using #if, #ifdef, #ifndef, #else, and #endif.

  #define DEBUG
  int main() {
  #ifdef DEBUG
   printf("Debug mode\n");
  #else
   printf("Release mode\n");
  #endif
   return 0;
  }

Standard Libraries

• stdio.h :
  • Provides functions for input and output operations.

  #include 
  printf("Hello, World!");

• stdlib.h :
  • Provides functions for memory allocation, process control, conversions, and others.

  #include 
  int *ptr = (int *)malloc(sizeof(int) * 5);
  free(ptr);

• string.h :
  • Provides functions for handling strings.

  #include 
  char str1[20] = "Hello";
  char str2[20];
  strcpy(str2, str1); // Copies str1 to str2
  printf("%s", str2);

• math.h :
  • Provides mathematical functions.

  #include 
  double result = sqrt(16.0);
  printf("Square root: %f", result);

Summary

C is a powerful and versatile programming language that provides low-level access to memory and system resources. Understanding its basic syntax, control structures, functions, data structures, file I/O, memory management, and standard libraries is essential for developing efficient and effective programs. C is widely used in system programming, embedded systems, and performance-critical applications.