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#include <stdio.h>  // Standard input/output header

// Basic program structure
int main() {
    // Program logic goes here
    printf("Hello, World!\n");
    return 0;  // Mandatory return for main function
}

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// Integer Types
short           // 16-bit integer (-32,768 to 32,767)
int             // Standard integer (-2,147,483,648 to 2,147,483,647)
long            // Long integer
long long       // Extended long integer

// Floating Point Types
float           // Single-precision floating point
double          // Double-precision floating point
long double     // Extended precision floating point

// Character Types
char            // 8-bit character
signed char     // Signed character
unsigned char   // Unsigned character

// Boolean (in C99 and later)
_Bool           // Boolean type (0 or 1)

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// Pointers
int *ptr;       // Pointer to integer
char *str;      // Pointer to character (string)

// Arrays
int arr[10];    // Fixed-size integer array
char name[50];  // Character array (string)

// Structures
struct Person {
    char name[50];
    int age;
    float height;
};

// Unions
union Data {
    int i;
    float f;
    char str[20];
};

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// Variable Declaration
int age = 30;           // Initialized variable
const float PI = 3.14;  // Constant value

// Type Qualifiers
volatile int sensor;    // Can change unexpectedly
static int count = 0;   // Retains value between function calls
extern int global;      // Declares variable defined elsewhere

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int a = 10, b = 5;
int sum = a + b;        // Addition
int diff = a - b;       // Subtraction
int prod = a * b;       // Multiplication
int div = a / b;        // Division
int mod = a % b;        // Modulus

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a == b;  // Equal to
a != b;  // Not equal to
a > b;   // Greater than
a < b;   // Less than
a >= b;  // Greater than or equal to
a <= b;  // Less than or equal to

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int x = 1, y = 0;
x && y;  // Logical AND
x || y;  // Logical OR
!x;      // Logical NOT

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a & b;   // Bitwise AND
a | b;   // Bitwise OR
a ^ b;   // Bitwise XOR
~a;      // Bitwise NOT
a << 2;  // Left shift
a >> 2;  // Right shift

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// If-Else
if (condition) {
    // Code if true
} else if (another_condition) {
    // Alternative condition
} else {
    // Default case
}

// Ternary Operator
int result = (x > y) ? x : y;  // Conditional assignment

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// For Loop
for (int i = 0; i < 10; i++) {
    // Repeated code
}

// While Loop
while (condition) {
    // Repeated code
}

// Do-While Loop
do {
    // Always executes at least once
} while (condition);

// Break and Continue
break;      // Exit loop
continue;   // Skip current iteration

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// Function Declaration
int add(int a, int b) {
    return a + b;
}

// Function Pointer
int (*operation)(int, int);

// Variadic Functions
#include <stdarg.h>
int sum_numbers(int count, ...) {
    va_list args;
    va_start(args, count);
    
    int sum = 0;
    for (int i = 0; i < count; i++) {
        sum += va_arg(args, int);
    }
    
    va_end(args);
    return sum;
}

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// Dynamic Memory Allocation
int *arr = malloc(10 * sizeof(int));  // Allocate memory
if (arr == NULL) {
    // Handle allocation failure
}

// Resizing Memory
arr = realloc(arr, 20 * sizeof(int));

// Freeing Memory
free(arr);

// Calloc for Zero-Initialized Memory
int *zeroed_arr = calloc(10, sizeof(int));

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#include <stdio.h>      // Include standard library
#define MAX_SIZE 100    // Constant definition
#define SQUARE(x) ((x) * (x))  // Macro function

#ifdef DEBUG
    printf("Debug mode\n");
#endif

#ifndef HEADER_H
#define HEADER_H
    // Header file contents
#endif

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FILE *file = fopen("example.txt", "r");  // Open file
if (file == NULL) {
    // Handle file open error
}

char buffer[100];
fgets(buffer, sizeof(buffer), file);  // Read line
fprintf(file, "Writing to file\n");   // Write to file

fclose(file);  // Close file

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#include <errno.h>
#include <string.h>

if (some_function() == -1) {
    printf("Error: %s\n", strerror(errno));
}

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// Structure
struct Student {
    char name[50];
    int age;
    float gpa;
};

// Typedef for easier type definition
typedef struct {
    int x, y;
} Point;

// Union
union Data {
    int i;
    float f;
    char str[20];
};

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enum Days {
    MONDAY,     // 0
    TUESDAY,    // 1
    WEDNESDAY,  // 2
    // ...
};

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# Compile with gcc
gcc -o program program.c

# Compile with warnings
gcc -Wall -Wextra -o program program.c

# Debug build
gcc -g -o program program.c