1. Multi-dimentional arrays

int matrix[3][2] = { {1, 2}, {3,4}, {5,6}};          <draw picture of matrix>
int *p = &matrix[0][0];

for (i = 0; i < 3; i ++) {
	for (j = 0; j < 2; j++) {
		sum += matrix[i][j];
	}
}

for (i = 0; i < 3 * 2; i++) {
	sum += p[i]; or sum += *(p+i);
}


2. 2D array vs. array of  pointers

int m[3][2];
int *n[3];

<draw picture of difference>
m:|_|_|_|_|_|_|_|
n: |_|_|_|


char *names1[3] = {"alice","bob","clark"};
char names2[3][10] = {"alice","bob","clark"};

names1[3][1] type and value?
names2[3][1] type and value?

3. structure

struct student {
	int id;
	char *name;
}

struct student s;
struct student *sp;

s.id = 1;
s.name = "alice";
sp = &s;
sp->id = 3;
printf("id %d, name %s\n", s.id, s.name);

To make things simpler,
typedef struct {
	int id;
	char *name;
} student;

student s;
student *sp;

sp = &s; //pointer to a struct
sp->id = 0;
sp->name = NULL;

4. A linked list
#include <stdio.h>
typedef struct {
	int key;
	char *value;
	struct node *next;
} node;

node *head = NULL;

void
push(node *n)
{
	n->next = head;
	head = n;
}

node *
pop() {
	node *n = head;
	if (n) {
		head = n->next;
	}
}

void
main()
{
	node n1,n2;
	n1.key = 1;
	n1.value = "hello";
	n2.key = 2;
	n2.value = "world";
	push(&n1);
	push(&n2);
}

5. malloc
Global variables are allocated space before program execution.
Local variables are allocated space at the entrace of a function/block and deallocated space upon exit.
Allocate space dynamically on the heap (and have it persist across functions/blocks)?

#include <stdlib.h>

node *
newNode(int key, char *value) {
	node *n = (node *)malloc(sizeof(node));
	n->key = key;
	n->value = (char *)malloc(5000);
	return n;
}

void
push(node *n) {
	n->number = x;
	n->next = head;
	head = n;
}

void
main()
{
	for (int i = 0; i < 1000000; i++) {
		n = newNode(i, "hello");
		push(n);
		n = pop();
		free(n);
	}
	
}