C Programming: Data Types, Memory & Strings

// Basic pointer and address demonstration
#include <stdio.h>

int main() {
    int n1 = 4, n2 = 8;
    int *pt1 = &n1, *pt2 = &n2;
    char c1 = 'A', c2 = 'B', c6;
    char *pc1 = &c1, *pc2 = &c2, *pc3 = &c6;
    
    // Print addresses and values
    printf("c1 address = %p, c1 value = %c\n", pc1, *pc1);
    printf("c2 address = %p, c2 value = %c\n", pc2, *pc2);
    printf("n1 address = %p, n1 value = %d\n", pt1, *pt1);
    printf("n2 address = %p, n2 value = %d\n", pt2, *pt2);
    
    return 0;
}

// Pointer arithmetic and memory addresses
#include <stdio.h>

int main() {
    int arr[] = {10, 20, 30, 40};
    int *ptr = arr;
    
    // Show how array elements are stored in consecutive memory
    for(int i = 0; i < 4; i++) {
        printf("arr[%d] = %d, address = %p\n", 
               i, *(ptr + i), (ptr + i));
    }
    
    // Show byte-level addressing
    char *byte_ptr = (char*)ptr;
    printf("\nByte-by-byte view of first integer:\n");
    for(int i = 0; i < sizeof(int); i++) {
        printf("Byte %d: %02X (address %p)\n", 
               i, *(byte_ptr + i), (byte_ptr + i));
    }
    
    return 0;
}

// C-Style String Examples
#include <stdio.h>
#include <string.h>

int main() {
    // Different ways to declare strings
    char str1[] = "Hello";           // Array on stack
    char *str2 = "World";           // Pointer to string literal
    char str3[20];                   // Uninitialized array
    char str4[10] = {'T', 'e', 's', 't', '\0'}; // Character array
    
    // Show string properties
    printf("str1 = \"%s\", length = %zu\n", str1, strlen(str1));
    printf("str2 = \"%s\", length = %zu\n", str2, strlen(str2));
    printf("str4 = \"%s\", length = %zu\n", str4, strlen(str4));
    
    // String operations
    strcpy(str3, "Copied");
    printf("After strcpy: str3 = \"%s\"\n", str3);
    
    strcat(str3, " String");
    printf("After strcat: str3 = \"%s\"\n", str3);
    
    // Character-by-character access
    printf("\nCharacter-by-character access of str1:\n");
    for(int i = 0; str1[i] != '\0'; i++) {
        printf("str1[%d] = '%c' (ASCII %d) at address %p\n", 
               i, str1[i], str1[i], &str1[i]);
    }
    
    return 0;
}

// Advanced String Operations
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

// Custom string length function
int my_strlen(const char *str) {
    int count = 0;
    while(*str != '\0') {
        count++;
        str++;
    }
    return count;
}

// Custom string copy function
char* my_strcpy(char *dest, const char *src) {
    char *original_dest = dest;
    while(*src != '\0') {
        *dest = *src;
        dest++;
        src++;
    }
    *dest = '\0'; // Don't forget null terminator!
    return original_dest;
}

int main() {
    char source[] = "Programming";
    char destination[20];
    
    printf("Source length (custom): %d\n", my_strlen(source));
    printf("Source length (library): %zu\n", strlen(source));
    
    my_strcpy(destination, source);
    printf("Copied string: %s\n", destination);
    
    // Dynamic string allocation
    char *dynamic_str = malloc(50 * sizeof(char));
    strcpy(dynamic_str, "Dynamic Memory");
    printf("Dynamic string: %s\n", dynamic_str);
    free(dynamic_str); // Don't forget to free!
    
    return 0;
}