Will it result in to an error if a header file is included twice?

struct emp
{
    int ecode;
    struct emp *e;
};

#include<stdio.h>

int main()
{
    union a
    {
        int i;
        char ch[2];
    };
    union a z1 = {512};
    union a z2 = {0, 2};
    return 0;
}

struct emp
{
    int ecode;
    struct emp e;
};

/* sample.c */
#include<stdio.h>

int main(int argc, char *argv[])
{
    printf("%c", **++argv);
    return 0;
}

#include<stdio.h>

int main()
{
    char far *near *ptr1;
    char far *far *ptr2;
    char far *huge *ptr3;
    printf("%d, %d, %d\n", sizeof(ptr1), sizeof(ptr2), sizeof(ptr3));
    return 0;
}

#include<stdio.h>

int main()
{
    char huge *near *far *ptr1;
    char near *far *huge *ptr2;
    char far *huge *near *ptr3;
    printf("%d, %d, %d\n", sizeof(ptr1), sizeof(*ptr2), sizeof(**ptr3));
    return 0;
}

#include<stdio.h>
typedef void v;
typedef int i;

int main()
{
    v fun(i, i);
    fun(2, 3);
    return 0;
}
v fun(i a, i b)
{
    i s=2;
    float i;
    printf("%d,", sizeof(i));
    printf(" %d", a*b*s);
}

/* myprog.c */
#include<stdio.h>
#include<stdlib.h>

int main(int argc, char **argv)
{
    int i, j=0;
    for(i=0; i<argc; i++)
        j = j+atoi(argv[i]);
    printf("%d\n", j);
    return 0;
}