week4class2 Practice Manipulating Pointer

#include <stdio.h>
int main()
{
 //change the vaule by pointer
 int i = 10;
 int *p;
 p = &i;
 *p = 8;
 //i must be 8
 printf("*p = 8 // i = %d\n", i);
 //reduce the vaule using (*p)-- ,value is changed after printing
 (*p)--;
 //i must be 7
 printf("(*p)-- // i = %d\n\n", i);
 //check the index
 int a1[10] = { 0 };
 int *p1;
 p1 = a1;
 printf("before *p1++ = %d\n" ,p1);
 *p1++ = 1;
 printf("*p1++ = 1\n");
 for (int j = 0; j < 10; j++) {
  printf("a1[%d] vaule = %d\n",j, a1[j]);
 }
 printf("after *p1++ = %d\n\n" ,p1);
 //pointer priority is higher than ++
 /*
  1. pointer addree ++
  (*p1++)
   */

 int a2[10] = { 0 };
 int *p2;
 p2 = a2;

 printf("before *++p2 = %d\n" ,p2);
 *++p2 = 1;
 printf("*++p2 = 1\n" );
 for (int j = 0; j < 10; j++) {
  printf("a2[%d] vaule = %d\n", j, a2[j]);
 }
 printf("after *++p2 = %d\n\n" ,p2);
 /*1.  p is changed to a[1] = p++
  2. *p is changed to 1
  ++ operates twice
  (*++p2) = 1 is equal to p2 = P2 + 1  and (*p2) == (*p2) + 1
 */

 int a3[10] = { 0 };
 int *p3;
 p3 = a3;

 printf("before (*p3)++ = %d\n" ,p3);
 (*p3)++;
 for (int j = 0; j < 10; j++) {
  printf("a3[%d] vaule = %d\n", j, a3[j]);
 }
 printf("after (*p3)++ = %d\n\n" ,p3);
 /* print *p3 and increase the pointer value*/

 int a4[10] = { 0 };
 int *p4;
 p4 = a4;

 printf("before ++*(p4+1) = %d\n" ,p4);
 ++*(p4+1);
 for (int j = 0; j < 10; j++) {
  printf("a4[%d] vaule = %d\n", j, a4[j]);
 }
 printf("after ++*(p4+1) = %d\n\n" ,p4);
 /*1.p is added 1 size of int
 2.a4[1]'s vaule increase to 1
 3. nochange for pointer value

 ++*(p4+1) is equal to p4 + 1 and a4[1] = a4[1] + 1
 */

 int a5[10] = { 0 };
 int *p5;
 p5 = a5;

 printf("before (*(p5+1))++ = %d\n" ,p5);
 (*(p5+1))++;
 for (int j = 0; j < 10; j++) {
  printf("a5[%d] vaule = %d\n", j, a5[j]);
 }
 printf("after (*(p5+1))++ = %d\n\n" ,p5);
 /* a5[1] = 1
 1.p5 is added 4 bit temperaily in this line => p5 = a5[1]
 2. *p5 is added 1 => a5[1] = 1;
 3. p5 doesn't changed

 this line, we just got a access to p5 + 1 but didn't changed vaule of a5
 */
}

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