Compound Types

C has compound types like:

• Array
• Struct
• Union
• Enumeration
• String, basically an array of characters

Array

An array is a collection of items stored at contiguous memory locations. Elements in an array can be accessed randomly using indexes.

int a[5];
int b[] = {0,1,2,3,4};

size_t len = sizeof(a) / sizeof(a[0]);
for(size_t i = 0; i < len; i++) {
    a[i] = i;
}

printf("%d\n", a[2]);

Strings

In C, a string is an array of char data, and terminated with the extra invisible \0 char.

For example:

#include <stdio.h>
#include <string.h>

int main() {
    // Declaration and initialization of a string
    char greeting[] = "Hello, World!";
    char *s = "Hi, Again!";

    // Display the string using printf
    printf("String: %s\n", greeting);
    printf("String: %s\n", s); // Output: Hi, Again!

    // Calculate and display the length of the string
    int length = strlen(greeting);
    printf("Length of the string: %d\n", length);

    // Access individual characters in the string
    printf("First character: %c\n", greeting[0]);  // Output: H
    printf("Third character: %c\n", greeting[2]);  // Output: l

    // Modify a character in the string
    greeting[7] = 'Y';
    printf("Modified string: %s\n", greeting);  // Output: Hello, Yorld!

    return 0;
}

Enumerations

Enumerations in C provide a way to create a named list of integer constants. Each constant in the enum has an associated integer value, and these values are assigned automatically by the compiler.

#include <stdio.h>

enum Color {
    RED,    // 0
    GREEN,  // 1
    BLUE    // 2
};

int main() {
    enum Color favoriteColor = BLUE;
    printf("Favorite color is %d\n", favoriteColor);
    // Favorite color is 2
    return 0;
}

Structs

In C, structs (structures) allow you to group variables of different types under a single name. They are user defined data storage objects containing public members by default.

#include <stdio.h>
#include <string.h>

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

int main() {
    struct Person person1;

    strcpy(person1.name, "Lite Rank");
    person1.age = 30;
    person1.height = 175.5;

    printf("Name: %s\n", person1.name);
    // Name: Lite Rank
    printf("Age: %d\n", person1.age);
    printf("Height: %.2f\n", person1.height);

    return 0;
}

Union

A union is a special data type that allows storing different data types in the same memory location. The size of a union is determined by the largest member's size. Unions provide an efficient way of using the same memory location for multiple purposes.

#include <stdio.h>

union Data {
    int intValue;
    float floatValue;
    char stringValue[20];
};

int main() {
    union Data data;

    data.intValue = 42;
    printf("Integer value: %d\n", data.intValue);

    data.floatValue = 3.14;
    printf("Float value: %.2f\n", data.floatValue);

    strcpy(data.stringValue, "Hello, Union!");
    printf("String value: %s\n", data.stringValue);

    printf("After reassignment:\n");
    printf("Integer value: %d\n", data.intValue);
    printf("Float value: %.2f\n", data.floatValue);
    printf("String value: %s\n", data.stringValue);

    return 0;
}

Code Challenge

Write a C program that uses a union to determine the size of various data types (int, float, double, char) without using the sizeof operator.