Estructuras en C

¿Qué es una estructura?  
Una estructura es una palabra clave que crea un tipo de datos definido por el usuario en C/C++. Una estructura crea un tipo de datos que se puede usar para agrupar elementos de tipos posiblemente diferentes en un solo tipo. 
 

struct address
{
   char name[50];
   char street[100];
   char city[50];
   char state[20];
   int pin;
};

// A variable declaration with structure declaration.
struct Point
{
   int x, y;
} p1;  // The variable p1 is declared with 'Point'
 
 
// A variable declaration like basic data types
struct Point
{
   int x, y;
};
 
int main()
{
   struct Point p1;  // The variable p1 is declared like a normal variable
}

struct Point
{
   int x = 0;  // COMPILER ERROR:  cannot initialize members here
   int y = 0;  // COMPILER ERROR:  cannot initialize members here
};

struct Point
{
   int x, y;
};
 
int main()
{
   // A valid initialization. member x gets value 0 and y
   // gets value 1.  The order of declaration is followed.
   struct Point p1 = {0, 1};
}

#include<stdio.h>
 
struct Point
{
   int x, y;
};
 
int main()
{
   struct Point p1 = {0, 1};
 
   // Accessing members of point p1
   p1.x = 20;
   printf ("x = %d, y = %d", p1.x, p1.y);
 
   return 0;
}

#include<stdio.h>
 
struct Point
{
   int x, y, z;
};
 
int main()
{
   // Examples of initialization using designated initialization
   struct Point p1 = {.y = 0, .z = 1, .x = 2};
   struct Point p2 = {.x = 20};
 
   printf ("x = %d, y = %d, z = %d\n", p1.x, p1.y, p1.z);
   printf ("x = %d", p2.x);
   return 0;
}

#include<stdio.h>
 
struct Point
{
   int x, y;
};
 
int main()
{
   // Create an array of structures
   struct Point arr[10];
 
   // Access array members
   arr[0].x = 10;
   arr[0].y = 20;
 
   printf("%d %d", arr[0].x, arr[0].y);
   return 0;
}

#include<stdio.h>
 
struct Point
{
   int x, y;
};
 
int main()
{
   struct Point p1 = {1, 2};
 
   // p2 is a pointer to structure p1
   struct Point *p2 = &p1;
 
   // Accessing structure members using structure pointer
   printf("%d %d", p2->x, p2->y);
   return 0;
}

struct number
{
    float x;
};
int main()
{
    struct number n1,n2,n3;
    n1.x=4;
    n2.x=3;
    n3=n1+n2;
    return 0;
}
 
/*Output:
 
prog.c: In function 'main':
prog.c:10:7: error:
invalid operands to binary + (have 'struct number' and 'struct number')
  n3=n1+n2;
 
*/

// Use of airthmatic operator in structure
 
#include <stdio.h>
 
struct number {
    float x;
};
int main()
{
    struct number n1,n2,n3;
    n1.x=4;
    n2.x=3;
    n3.x=(n1.x)+(n2.x);
    printf("\n%f",n3.x);
    return 0;
}