Structures

In C structures defined using the struct keyword are a very important concept as they allow for grouping of elements very similarly to classes in other languages they just don’t include functions. For example a date, month, day, year. can then create variables as type struct date. memory is allocated 3 variables inside. can access member variables with. so today.year for example can also assign initialcompound literal can assign values after initilation like (struct date) {1,2,3} or specify the specific values with .month=9for only one time thing. can initialize structs like arrays with {7,2,2015}. or just the frist 2 or can do {.month=12}

Unnamed structs

Unnamed structures can be used if you know that you only need one instance of it at all times which can be useful for constants.


    struct /* No name */ {
        float x;
        float y;
    } point;
 
    point.x = 42;

Array of structs

Can then do all the normal things you would expect to be able to do with an array.


struct Student
{
    int rollNumber;
    char studentName[10];
    float percentage;
};
struct Student studentRecord[5];

Nested structs

A nested structure in C is a structure within structure. One structure can be declared inside another structure in the same way structure members are declared inside a structure.


struct Date
{
    int day;
    int month;
    int year;
};
struct Time
{
    int hours;
    int minutes;
    int seconds;
};
struct DateTime
{
    struct Date date;
    struct Time time;
}

Pointers to structs

You can have pointers to struct variables. The important thing to know here is that there is a shorthand for accessing the data by usign the -\> operator.


#include<stdio.h>
 
struct dog
{
    char name[10];
    char breed[10];
    int age;
    char color[10];
};
 
int main()
{
    struct dog my_dog = {"tyke", "Bulldog", 5, "white"};
    struct dog *ptr_dog;
    ptr_dog = &my_dog;
 
    printf("Dog's name: %s\n", (*ptr_dog).name); // instead of having to do this
    printf("Dog's breed: %s\n", ptr_dog->breed); // you can do this
    printf("Dog's age: %d\n", ptr_dog->age);
    printf("Dog's color: %s\n", ptr_dog->color);
 
    // changing the name of dog from tyke to jack
    strcpy(ptr_dog->name, "jack");
 
    // increasing age of dog by 1 year
    ptr_dog->age++;
 
    printf("Dog's new name is: %s\n", ptr_dog->name);
    printf("Dog's age is: %d\n", ptr_dog->age);
 
    return 0;
}

typdef

The typedef keyword is used in C to assign alternative names to existing datatypes. This can be especially powerfull when combined with structs.can be used to give a type a new name. so typedef unsigned char BYTE; BYTE can then be used as an allias. this can become very powerful with structs.


#include <stdio.h>
 
typedef struct Point
{
    double x;
    double y;
} Point; // can have the same name
 
struct date
{
    unsigned short day;
    unsigned short month;
    unsigned int year;
};
typedef struct date Date;
 
typedef unsigned char byte;
 
int main(void)
{
    Point origin = {0, 0};
    struct date today = {1, 4, 2022};
    Date tomorrow = {2, 4, 2022};
    byte intSize = sizeof(int);
 
    printf("The origin is: (%f/%f)\n", origin.x, origin.y);
    printf("Today is %d/%d/%d\n", today.day, today.month, today.year);
    printf("Tommorrow is %d/%d/%d\n", tomorrow.day, tomorrow.month, tomorrow.year);
    printf("On my computer an int takes up %d bytes.\n", intSize);
 
    return 0;
}

output


The origin is: (0.000000/0.000000)
Today is 1/4/2022
Tommorrow is 2/4/2022
On my computer an int takes up 4 bytes.