Examples of C Code. Files are on Canvas Files/website/lec/l-c

---------- array.c ---------------------------------------
#include "kernel/types.h"
#include "user/user.h"

int a[3] = {1, 2, 3};    // an array of 3 int's
char b[3] = {'a', 'b', 'c'};  // an array of 3 char's
	
int
main(int ac, char **av)
{

  // first element is at index 0
  printf("%d\n", a[0]);
  
  a[1] += 1;  // use index access
  *(a+2) = 5; // pointer access
  
  printf("%d %d\n", a[1], a[2]);

  // pointers to array elements
  printf("a %p a1 %p a2 %p a2 %p\n", a, a+1, a+2, &a[2]);

  // pointer arithmetic uses type
  printf("%p %p\n", b, b+1);
  
  return 0;
}
---------- ptr.c ---------------------------------------
#include "kernel/types.h"
#include "user/user.h"

int g = 3;
	
int
main(int ac, char **av)
{
  int l = 5;   // local variables don't have a default value
  int *p, *q;
  
  // take address of variable
  p = &g;
  q = &l;
  printf("p %p q %p\n", p, q);

  // assign using pointer
  *p = 11;
  *q = 13;
  printf("g %d l %d\n", g, l);

  // struct
  struct two {
    int a;
    int b;
  } s;
  s.a = 10;
  struct two *ptr = &s;
  printf("%d %d\n", s.a, ptr->a);

  // can take address of any variable
  int **pp;
  pp = &p;    // take address of a pointer variable
  printf("pp %p %p %d\n", pp, *pp, **pp);

  int (*f)(int, char **);
  f = &main;  // take address of a function<
  printf("main: %p\n", f);

  return 0;
}
---------- str.c ---------------------------------------
#include "kernel/types.h"
#include "user/user.h"

char *s = "123";
	
int
main(int ac, char **av)
{
  char s1[4] = {'1', '2', '3', '\0'}; 

  // s and s1 are strings
  printf("s %s s1 %s\n", s, s1);

  // can use index or pointer access
  printf("%c %c\n", s[0], *s);
  printf("%c %c\n", s[2], *(s+2));

  // read beyond str end; DON'T DO THIS
  printf("%x %p %p\n", s1[4], s1, &s1[4]);

  // write beyond str end; DON'T DO THIS
  s1[4] = 'D';
  
  return 0;
}