What do the following declaration signify?

void (*cmp)();

char *ptr[3]();

char (*ptr)*[3];

char (*ptr[3])();

char (*ptr)[3];

void *cmp();

char *scr;

void *(ptr)*int;

void *(*ptr)()

void *(*ptr)(*)

void (*ptr)()

char **argv;

int *ptr[30];

#include<stdio.h>
int main()
{
    extern int i;
    i = 20;
    printf("%d\n", sizeof(i));
    return 0;
}

#include<stdio.h>
int main()
{
    enum status { pass, fail, atkt};
    enum status stud1, stud2, stud3;
    stud1 = pass;
    stud2 = atkt;
    stud3 = fail;
    printf("%d, %d, %d\n", stud1, stud2, stud3);
    return 0;
}

#include<stdio.h>
int main()
{
    extern int a;
    printf("%d\n", a);
    return 0;
}
int a=20;

#include<stdio.h>
int X=40;
int main()
{
    int X=20;
    printf("%d\n", X);
    return 0;
}