// Pantea Aria

// static memories - they get released once the program finishes.

// you can allocate memory whenever you want and free that whenver you want - Dynamic memory
// malloc to allocate dynamic memory

#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>
struct student {
    int zid;
    double marks;
};
struct point {
    int x, y;

};

int main(void) {
    
    // grab dynamic memory for one integer
    // allocating 4 bytes of heap and return the address into p from stack memory
    int *p = malloc(sizeof(int));

    // assign 20 to that memory from head
    // dereferencing
    *p = 20;
    
    // print the value in the memory
    printf("the value is %d\n", *p);  //20
    
    // if you don't need that memory, then release it
    free(p);
    // *p = 90;   // INVALID

    // dynamic array of int
    // 10 integer after each other in heap
    p = malloc(10 * sizeof(int));

    // assign 10 to 19 to them
    for(int i = 10; i < 20; i++) {
        p[i - 10] = i;
    }
    
    // print out all values in the array
    int i = 0;
    while (i < 10) {
        printf ("%d ", p[i]);
        i++;
    }
    free(p);   

    // dynamic structure from heap
    // define struct student before main
    // allocate memory from heap for 1 student
    struct student *q = malloc(sizeof(struct student));
    // assign value to zid - dereferencing a pointer to structure
    q->zid = 123456;
    // assign value to marks 
    q->marks = 56.6;
    // print out the values
    printf("%d %lf", q->zid, q->marks);
    
    // release it
    free(q);


    // allocate memory for one character
    char *ch = malloc(sizeof(char));

    // assign some value to it
    *ch = 'A';
    // check if upper or lowercase and print out
    if (isupper(*ch)) {
        printf("\n%c is upper\n", *ch);
    
    } else {
        printf("\n%c is lower", *ch);
    }
    free(ch);
  
    // dynamic structure
    // struct point - create a dynamic point (x, y) with a function, 
    struct point *st = malloc(sizeof(struct point));
    // print x, y with another function
    st->x = 10;
    st->y = 9;
    printf("x and y are %d and %d\n", st->x, st->y);
    free (st);

    // allocate memory for 5 points
    st = malloc(5 * sizeof(struct point));
    if (st == NULL) {
        return 1;
    }
    st[0].x = 8;
    st[0].y = 0;
    // have a loop st[i].x , ....
    
    return 0;

}