以下程序的输出?
#include
int main()
{
int *ptr;
int x;
ptr = &x;
*ptr = 0;
printf(" x = %d\n", x);
printf(" *ptr = %d\n", *ptr);
*ptr += 5;
printf(" x = %d\n", x);
printf(" *ptr = %d\n", *ptr);
(*ptr)++;
printf(" x = %d\n", x);
printf(" *ptr = %d\n", *ptr);
return 0;
}
(A) x = 0
* ptr = 0
x = 5
* ptr = 5
x = 6
* ptr = 6
(B) x =垃圾值
* ptr = 0
x =垃圾值
* ptr = 5
x =垃圾值
* ptr = 6
(C) x = 0
* ptr = 0
x = 5
* ptr = 5
x =垃圾值
* ptr =垃圾值
(D) x = 0
* ptr = 0
x = 0
* ptr = 0
x = 0
* ptr = 0答案： (A)
说明：请参阅以下注释以获取说明。
int *ptr; /* Note: the use of * here is not for dereferencing,
it is for data type int */
int x;
ptr = &x; /* ptr now points to x (or ptr is equal to address of x) */
*ptr = 0; /* set value ate ptr to 0 or set x to zero */
printf(" x = %d\n", x); /* prints x = 0 */
printf(" *ptr = %d\n", *ptr); /* prints *ptr = 0 */
*ptr += 5; /* increment the value at ptr by 5 */
printf(" x = %d\n", x); /* prints x = 5 */
printf(" *ptr = %d\n", *ptr); /* prints *ptr = 5 */
(*ptr)++; /* increment the value at ptr by 1 */
printf(" x = %d\n", x); /* prints x = 6 */
printf(" *ptr = %d\n", *ptr); /* prints *ptr = 6 */
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