Struct in C

Struct

Aggregating associated data into single variable

void main(){
	Box box;
	Circle c;
	box.with = 10;
	box.length = 30;
	box.heigth = 10;
	c.radius = 10;
}

Box
Width length height

Circle
radius

Struct in C

The idea

I want to describe a box. I need variables for the width, length, and height.

I can use three variable, but would't it be better if i had a single variale to describe a box?

That variable can have three parts, the width, length, and height.

Box
Width length height

Struct in C

Structs

A struct (short for structure) in C is grouping of variable together into a single type

Syntax

struct nameOfStruct{
	type member;
	type memer;
	....	
};

Note the semicolon at the end.

To declare a variable: struct nameOfStruct variable_name;

Struct in C

Example

Box
Width length height

Circle
radius

//Data structure defination
struct Box{
	int width;
	int length;
	int height;	
};
struct Circle{
	double radius;
};
void main(){
	//Declare variables
	struct Box b;
	struct Circle c;
}

Struct in C

Example

struct Box{
	int width;
	int height;
	int length;	
};

Box
Width length height

void main(){
	struct Box b;
	//You can assign values to each member
	b.width = 10;
	b.length = 30;
	b.height = 10;
}

We use a period "." to get the elements of a struct.

If x is a struct, x.width is an element in a struct.

Struct in C

Another Example

struct BankRecord{
	char name[50];
	float balance;	
};
struct BankRecord billsAcc;

You can use mixed data types within the struct (int, float, char[])

Struct in C

Accessing Values

Access values in a struct using period: "."

struct BankRecord{
	char name[50];
	float balance;	
};
struct BankRecord billsAcc;
printf("My balance is: %f", billsAcc.balance);
float bal = billsAcc.balance;

Struct in C

Assign Values using scanf

struct BankRecord{
	char name[50];
	float balance;
};
void main(){
	struct BankRecord acc; //create new bank record
	printf("Enter account name: ");
	scanf("%50s", acc.name);
	printf("Enter account balance: ");
	scanf("%f", &acc.balance);
}

Struct in C

Copy via =

You can set two struct type variables equal to each other and each element will be copied

struct Box{
	int width, length, height;
};
void main(){
	struct Box b, c;
	b.width = 5;
	b.length = 1;
	b.height = 2;
	c = b; //copies all elements of b to c
	printf("%d %d %d\n", c.width, c.length, c.height);
}

Struct in C

Passing Struct to a function

You can pass a struct to a function. All the elements are copied

If an element is a pointer, the pointer is copied but not what it points to!

void f(struct Box b){
	//do something
}

Struct in C

Using Structs in Functions

Write a program that

Prompts the user to enter the dimensions of 3D box and a circle.

Prints the volume of the box and area of the circle.

Sample run:

Enter the box dimensions (width, length, height): 1 2 3

Enter the radius of ther circle: 0.8

Box volume = 6

Circle are = 2.01

Struct in C

Program struct Box

struct Box{
	int width, height, length;
};
int getVolume(struct Box b){
	return b.width + b.height + b.length;
}
void main(){
	struct Box b;
	printf("Enter the box dimensions (width, length, height): ");
	scanf("%d %d %d", &b.width, &b.length, &b.height);
	printf("Box volume = %d\n", getVolume(b));
}

Struct in C

Note: == Comparision doesn't work

struct Box{
	int width, height, length;
};
void main(){
	struct Box b, c;
	b.width = 5, b.length = 1, b.height = 2;
	c = b;
	if(c == b){ //Error when you compile!
		printf("c and b are identical\n");
	}else{
		prinf("c and b are difference\n");
	}
}
//Error message: invalid operands to binary == (Have 'Box' and 'Box')

Struct in C

Create you own equality test

#include <stdbool&tg;
struct Box{
	int width, length, height;
};
bool isEqual(struct Box b, struct Box c){
	return b.width == c.width && b.length == c.length && b.height == c.height;
}

Struct in C

typedef

typedef is a way in C to give a name to a custom type.

Syntax: typedef type newName;

typedef int dollars;
typedef unsigned char byte;
//I can declare variable like
dolors d;
byte b, c;

It's as if the type already existed

Struct in C

typedef for Arrays

There is a special syntax for arrays:

typedef char names[40];
typedef double vector[4];
typedef double matrix4x4[4][4];
//Now, instead of:
double mat[4][4];
//I can do:
matrix4x4 mat;

Struct in C

Using Structs with Typedef

syntax:

typedef struct [nameOfStruct]{//optional
	type member;
	type member;
	...
}TypeName;

To declare a variable: TypeName variable_name

Struct in C

Example struct with typedef

Box
Width length height

Circle
radius

typedef struct{
	int width, height, length;	
}Box;
typedef struct{
	double radius;
}Circle;
void main(){
	Box b; //Instead of struct Box
	Circle c; //Instead of struct Circle
	b.with = 10;
	b.length = 30;
	b.height = 10;
	c.radius  10;
}

Struct in C

Arrays of structs

You can declare an array of a structure and minupalate each one

typedef struct{
	double radius;	
};
Circle circles[5];

Struct in C

Size of a Struct: sizeof

typedef struct{
	char name[10]; //8 bytes
	int age; // 4 bytes
	char gender;//1 bytes
}Student;
printf("Size of circle struct is %ld\n", sizeof(Student));

Struct in C

Pointers to structs

typedef struct{
	int width, length, height;
}Box;
Box b; //A variable of type Box
Box *c; //A pointer to a Box
double w;
b.width = 5;
b.height = 7;
b.length = 3;
c = &b; //Same as before
w = c->width;

To access the members of a struct, we use:

"."" for variable of the struct's type

"->" for a pointer to a struct

Struct in C

struct Concepts

typedef struct{
	double width, height;
}Box;
typedef struct{
	double radius;
}Circle;

Box b;
Circle c;
Box* pb;
Circle* pc;
pb = &b;
b.width = 3;
pb->width = 7;
pc = &c;
(*pc).radius = 9;