Pointer in C Language

#include<stdio.h>
main()
{
    float a = 10.2;
    int *p = a;
    printf("%d",*p);
}

#include<stdio.h>
main()
{
    int a[5] = {1, 2, 3, 4, 5};
    int *p = a;
    printf("%d\t%d\t%d\t%d\t",*p,0[a],a,p);
}

#include <stdio.h>
int arr[] = {1,2,3};
main()
{
    int *ptr; 
    ptr = arr;
    ptr = ptr+3;
    printf("%d",*ptr);
} 

#include <stdio.h>
void main()
{
    int const *p = 5;
    printf("%d", ++(*p));
}

#include<stdio.h>
main()
{
    struct std
    {
        int x = 3;
        char name[] = "hello";
    };
    struct std *s;
    printf("%d", s->x);
    printf("%s", s->name);
} 

#include <stdio.h>
main()
{
    register i = 5;
    char j[] = "hello";
    printf("%s %d", j, i);
}

int sum(int, int);
int (*s)(int, int);
s = sum;

#include <stdio.h>
int fun(int *a,int *b)
{
    *a = *a+*b;
    *b = *a-*b;
    *a = *a-*b;
}
main()
{
    int x = 10,y = 20;
    fun(&x,&y);
    printf("x= %d y = %d\n", x, y);
}