The C Language Basics

#include <stdio.h>  // Preprocessor directive

#define PI 3.14159  // Macro definition

// Global variable
int globalCount = 0;

// Function prototype
float calculateArea(float radius);

int main() {  // main function - entry point
    printf("Hello, World!\n");
    
    int localVar = 10;  // Local variable
    globalCount++;
    
    float area = calculateArea(5.0);
    printf("Area of circle: %.2f\n", area);
    
    return 0;  // Return statement
}

// User-defined function
float calculateArea(float radius) {
    return PI * radius * radius;
}

#include <stdio.h>
#include <limits.h>
#include <float.h>

int main() {
    printf("Data Type Sizes (in bytes):\n");
    printf("char: %zu\n", sizeof(char));
    printf("int: %zu\n", sizeof(int));
    printf("float: %zu\n", sizeof(float));
    printf("double: %zu\n", sizeof(double));
    
    printf("\nInteger Ranges:\n");
    printf("INT_MAX: %d\n", INT_MAX);
    printf("INT_MIN: %d\n", INT_MIN);
    
    printf("\nFloat Ranges:\n");
    printf("FLT_MAX: %e\n", FLT_MAX);
    printf("FLT_MIN: %e\n", FLT_MIN);
    
    // Examples
    char ch = 'A';
    int num = 100;
    float pi = 3.14159f;
    double e = 2.718281828459045;
    
    printf("\nValues: char=%c, int=%d, float=%.2f, double=%.15f\n",
           ch, num, pi, e);
    
    return 0;
}

#include <stdio.h>

#define MAX_SIZE 100  // Preprocessor constant (no semicolon)
#define PI 3.14159

int main() {
    // Variable declarations
    int age = 25;           // integer variable
    float salary = 45000.50; // float variable
    char grade = 'A';        // character variable
    
    // const variables
    const int DAYS_IN_WEEK = 7;
    const float TAX_RATE = 0.15;
    
    // Using constants
    int numbers[MAX_SIZE];  // Using #define constant
    
    printf("Age: %d\n", age);
    printf("Salary: %.2f\n", salary);
    printf("Grade: %c\n", grade);
    printf("Days in week: %d (const)\n", DAYS_IN_WEEK);
    printf("PI from #define: %.5f\n", PI);
    
    // Can modify variables
    age = 26;
    printf("Updated age: %d\n", age);
    
    // DAYS_IN_WEEK = 8;  // ERROR! Can't modify const
    
    return 0;
}

#include <stdio.h>

int main() {
    int a = 10, b = 3;
    
    // Arithmetic
    printf("Arithmetic:\n");
    printf("a + b = %d\n", a + b);
    printf("a - b = %d\n", a - b);
    printf("a * b = %d\n", a * b);
    printf("a / b = %d (integer division)\n", a / b);
    printf("a %% b = %d (modulo)\n", a % b);
    
    // Relational
    printf("\nRelational:\n");
    printf("a == b: %d\n", a == b);
    printf("a > b: %d\n", a > b);
    
    // Logical
    int x = 1, y = 0;
    printf("\nLogical:\n");
    printf("x && y: %d\n", x && y);
    printf("x || y: %d\n", x || y);
    printf("!x: %d\n", !x);
    
    // Bitwise
    printf("\nBitwise:\n");
    printf("a & b = %d\n", a & b);
    printf("a | b = %d\n", a | b);
    printf("a ^ b = %d\n", a ^ b);
    printf("~a = %d\n", ~a);
    printf("a << 1 = %d\n", a << 1);
    
    // Increment/Decrement
    int c = 5;
    printf("\nIncrement/Decrement:\n");
    printf("c++: %d (post-increment)\n", c++);
    printf("Now c: %d\n", c);
    printf("++c: %d (pre-increment)\n", ++c);
    
    // Ternary
    int max = (a > b) ? a : b;
    printf("\nTernary: max = %d\n", max);
    
    // sizeof
    printf("\nsizeof(int) = %zu bytes\n", sizeof(int));
    
    return 0;
}

#include <stdio.h>

int main() {
    int num = 5;
    
    // if-else
    printf("=== if-else ===\n");
    if(num > 0) {
        printf("%d is positive\n", num);
    } else if(num < 0) {
        printf("%d is negative\n", num);
    } else {
        printf("Zero\n");
    }
    
    // switch-case
    printf("\n=== switch-case ===\n");
    int choice = 2;
    switch(choice) {
        case 1:
            printf("Option 1 selected\n");
            break;
        case 2:
            printf("Option 2 selected\n");
            break;
        default:
            printf("Invalid option\n");
    }
    
    // for loop
    printf("\n=== for loop (1 to 5) ===\n");
    for(int i = 1; i <= 5; i++) {
        printf("%d ", i);
    }
    printf("\n");
    
    // while loop
    printf("\n=== while loop (countdown) ===\n");
    int count = 5;
    while(count > 0) {
        printf("%d ", count--);
    }
    printf("\n");
    
    // do-while loop
    printf("\n=== do-while (executes at least once) ===\n");
    int x = 10;
    do {
        printf("x = %d\n", x);
        x++;
    } while(x < 5);  // Condition false, but loop executed once
    
    // break and continue
    printf("\n=== break and continue ===\n");
    for(int i = 1; i <= 10; i++) {
        if(i == 5) continue;  // Skip 5
        if(i == 8) break;     // Stop at 8
        printf("%d ", i);
    }
    printf("\n");
    
    return 0;
}