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cpointersscanfampersand

Ampersand(&) and scanf in C?

I have the following multiple-choice question and I cannot figure out why (A) and (C) are incorrect, any explanation would be appreciated! The only correct answer in the following question is (B).

Which of the following is a correct usage of scanf?
(A) int i=0; scanf("%d", i);
(B) int i=0; int *p=&i; scanf("%d", p);
(C) char *s="1234567"; scanf("%3s", &s);
(D) char c; scanf("%c", c);

Solution

  • scanf wants a correct address where to store the result:

    (A) int i=0; scanf("%d", i);

    i is passed here by value, no address: wrong.

    (B) int i=0; int *p=&i; scanf("%d", p);

    p is a pointer to int, scanf can store its result here: right

    (C) char *s="1234567"; scanf("%3s", &s);

    &s is the address of a pointer to char *, you cannot store a string there: wrong

    (D) char c; scanf("%c", c);

    c is passed by value, not an address: wrong