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src/resources/programming/c.md
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316
src/resources/programming/c.md
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# C Programming Language Cheatsheet
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## Table of Contents
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- [Basic Structure](#basic-structure)
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- [Variables and Data Types](#variables-and-data-types)
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- [Memory Management](#memory-management)
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- [Binary Operators](#binary-operators)
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- [Assignment Shortcuts](#assignment-shortcuts)
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- [Standard Input/Output Functions](#standard-inputoutput-functions)
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- [Standard Library Functions](#standard-library-functions)
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- [Best Practices](#best-practices)
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- [Advanced Topics](#advanced-topics)
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## Basic Structure
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### Program Template
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```c
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/* comment to describe the program */
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#include <stdio.h>
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/* definitions */
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int main(int argc, char **argv) {
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/* variable declarations */
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/* program statements */
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}
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```
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### Naming Conventions
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Variable names must follow these rules:
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- Can contain uppercase letters (A to Z)
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- Can contain lowercase letters (a to z)
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- Can contain numbers (0 to 9)
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- Can contain underscores (_)
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- Cannot start with a number
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- Are case-sensitive
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## Variables and Data Types
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### Basic Data Types
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| Data Type | Description | Example Usage |
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|-----------|-------------|---------------|
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| int | Integer values | `int count = -1;` |
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| char | Character values | `char letter = 'A';` |
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| float | Floating point numbers | `float pi = 3.141f;` |
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| double | Double precision numbers | `double precise_pi = 3.14159265359;` |
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### Variable Declaration Examples
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```c
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int age;
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char initial;
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float temperature;
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double precise_measurement;
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int *pointer_to_int;
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char string_array[50];
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```
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## Memory Management
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### Dynamic Memory Allocation
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```c
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// Allocating memory
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int *array = (int *) malloc(sizeof(int) * 10);
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if (array == NULL) {
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/* handle allocation failure */
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}
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// Resizing memory
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int *newarray = (int *) realloc(array, sizeof(int) * 20);
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if (newarray == NULL) {
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/* handle reallocation failure */
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}
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array = newarray;
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// Freeing memory
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free(array);
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```
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### Memory Management Best Practices
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1. Always check for NULL after malloc/realloc
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2. Always free allocated memory when no longer needed
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3. Never free memory more than once
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4. Update pointers after reallocation
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5. Initialize pointers to NULL when declaring
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## Binary Operators
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### Bitwise Operations
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| Operator | Description | Example |
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|----------|-------------|----------|
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| a & b | Bitwise AND | `result = 5 & 3;` |
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| a \| b | Bitwise OR | `result = 5 \| 3;` |
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| a ^ b | Bitwise XOR | `result = 5 ^ 3;` |
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| a << n | Left shift | `result = 5 << 2;` |
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| a >> n | Right shift | `result = 5 >> 2;` |
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## Assignment Shortcuts
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### Compound Assignment Operators
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| Operator | Equivalent | Example |
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|----------|------------|---------|
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| += | a = a + b | `a += b;` |
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| -= | a = a - b | `a -= b;` |
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| *= | a = a * b | `a *= b;` |
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| /= | a = a / b | `a /= b;` |
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| %= | a = a % b | `a %= b;` |
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## Standard Input/Output Functions
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### Standard Streams
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| Stream | Description | Usage |
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|--------|-------------|-------|
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| stdin | Standard input | Reading user input |
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| stdout | Standard output | Normal program output |
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| stderr | Standard error | Error messages |
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### File Operations
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```c
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FILE *fopen(char *filename, char *mode);
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size_t fread(void *ptr, size_t size, size_t nitems, FILE *stream);
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int fclose(FILE *stream);
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```
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### Input/Output Functions
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```c
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// String output
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int puts(char *string);
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int printf(char *format, ...);
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int fprintf(FILE *stream, char *format);
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int sprintf(char *string, char *format);
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// Character input/output
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int getc(FILE *stream);
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int putc(int ch, FILE *stream);
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int getchar(void);
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int putchar(int ch);
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```
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## Standard Library Functions
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### Memory Management Functions
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```c
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void *malloc(size_t size);
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void *realloc(void *ptr, size_t newsize);
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void free(void *ptr);
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```
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### Sorting and Searching
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```c
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void qsort(void *array, size_t nitems, size_t size,
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int (*compar)(void *a, void *b));
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void *bsearch(void *key, void *array, size_t nitems,
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size_t size, int (*compar)(void *a, void *b));
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```
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### Random Number Generation
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```c
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void srand(unsigned int seed);
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int rand(void);
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```
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## Best Practices
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### Memory Management Guidelines
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1. Always initialize variables before use
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2. Check return values from memory allocation functions
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3. Free dynamically allocated memory
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4. Avoid memory leaks
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5. Use appropriate data types for variables
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### Code Organization
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1. Include necessary header files at the start
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2. Define constants and macros after headers
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3. Declare global variables (if needed) after definitions
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4. Define functions before use or provide prototypes
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5. Use meaningful variable and function names
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### Error Handling
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1. Always check return values of system calls
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2. Use stderr for error messages
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3. Implement proper error recovery mechanisms
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4. Clean up resources in error conditions
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5. Use appropriate error codes
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## Advanced Topics
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### Function Pointers
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```c
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// Declaration of a function pointer
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int (*operation)(int, int);
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// Example usage
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int add(int a, int b) {
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return a + b;
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}
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operation = &add;
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int result = (*operation)(5, 3);
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```
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### Structures and Unions
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```c
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struct Point {
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int x;
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int y;
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};
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union Data {
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int i;
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float f;
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char str[20];
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};
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```
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### Preprocessor Directives
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```c
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#define MAX_SIZE 100
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#define SQUARE(x) ((x) * (x))
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#ifdef DEBUG
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// Debug code
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#endif
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#ifndef HEADER_H
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#define HEADER_H
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// Header content
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#endif
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```
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### Type Definitions
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```c
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typedef unsigned long ulong;
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typedef struct Point Point;
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typedef void (*CallbackFunc)(void *data);
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```
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### Bit Fields
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```c
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struct Flags {
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unsigned int is_active : 1;
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unsigned int is_urgent : 1;
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unsigned int priority : 3;
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};
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```
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## Common Programming Patterns
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### Buffer Management
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```c
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#define BUFFER_SIZE 1024
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char buffer[BUFFER_SIZE];
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size_t bytes_read;
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// Safe reading
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if ((bytes_read = fread(buffer, 1, BUFFER_SIZE - 1, file)) > 0) {
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buffer[bytes_read] = '\0';
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}
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```
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### String Manipulation
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```c
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// String copy with bounds checking
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char dest[50];
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const char *src = "Hello, World!";
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strncpy(dest, src, sizeof(dest) - 1);
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dest[sizeof(dest) - 1] = '\0';
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```
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### Command Line Arguments
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```c
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int main(int argc, char **argv) {
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for (int i = 1; i < argc; i++) {
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printf("Argument %d: %s\n", i, argv[i]);
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}
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return 0;
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}
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```
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## Debugging Tips
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### Common Debugging Techniques
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1. Use printf debugging
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2. Check return values
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3. Validate pointer operations
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4. Monitor memory usage
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5. Use assert statements
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### Assert Usage
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```c
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#include <assert.h>
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void process_data(int *data, size_t size) {
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assert(data != NULL);
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assert(size > 0);
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// Process data
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}
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```
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## Performance Optimization
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### Optimization Techniques
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1. Use appropriate data structures
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2. Minimize memory allocation
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3. Optimize loops
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4. Use bitwise operations when applicable
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5. Consider cache efficiency
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### Example Optimizations
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```c
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// Optimized loop
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for (int i = 0; i < size; i++) {
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// Cache the value to avoid multiple array accesses
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int temp = array[i];
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if (temp > max) {
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max = temp;
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}
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}
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```
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