Example C code  -- focussing on use of pointers


/*  *********************  */

// rvalue and lvalue

int x;
int* p;
int** q;

x = 3;
p = &x;
q = &p;
printf("%d %d %d\n", x, *p, **q);


int y, z;

y = * p;

z = **q;


/* ***************** */

// swap function example
int swap (int *x, int *y) {
  int t = *x;
  *x = *y;
  *y = t;
  }
  
main() {
  int a = 3, b = 5;
  swap (&a, &b);
  // print (a, b)
  }
  
*/


/* ************  */
// a[i], *(a+i)

int[5] arr1 = {0, 10, 20, 30, 40};
int * arr2;
int i;

arr2 = arr1;

for (i = 0; i < 5; i++)
   printf( "%d %d\n", arr1[i], *(arr2 + i) );

/*
0 0
10 10
20 20
...
*/

char *fname = "abc";
char[] lname = "ABC";

printf("%s: \n", fname);
printf("%s: \n", lname);

/* http://scitechconnect.elsevier.com/why-write-code/?utm_source=socialmedia&utm_medium=compsci&utm_campaign=Why%20Write%20Code%3F&sf14216017=1 */

unsigned int n = 0x0A0B0C0D;
unsigned char c, d, *p;

c = (unsigned char) n;
p = (unsigned char *) &n;
d = *p


/*   function pointers  */

int addi (int x, int y) { return x + y; }
int subi (int x, int y) { return x - y; }

int useFunctionPtr (int a, int b, int (* fun) (int, int)) { return fun (a, b); }

int main () {
   int x = 3, y = 5, result;
   result = useFunctionPtr (x, y, &addi);
   // output result
   
   result = useFunctionPtr(x, y, &sub1);
   // output result
   }