Output of C Programs | Set 9

Predict the output of the below programs.

Question 1

int main() {  int c=5;  printf("%d\n%d\n%d", c, c <<= 2, c >>= 2);  getchar(); }

Output: Compiler dependent
Evaluation order of parameters is not defined by C standard and is dependent on compiler implementation. It is never safe to depend on the order of parameter evaluation. For example, a function call like above may very well behave differently from one compiler to another.

References:
http://gcc.gnu.org/onlinedocs/gcc/Non_002dbugs.html

Question 2

int main() {     char arr[] = {1, 2, 3};     char *p = arr;     if(&p == &arr)      printf("Same");     else      printf("Not same");     getchar(); }

Output: Not Same
&arr is an alias for &arr[0] and returns the address of the first element in array, but &p returns the address of pointer p.
Now try below program

int main() {     char arr[] = {1, 2, 3};     char *p = arr;     if(p == &arr)      printf("Same");     else      printf("Not same");     getchar(); }

Question 3

int main() {     char arr[] = {1, 2, 3};     char *p = arr;     printf(" %d ", sizeof(p));     printf(" %d ", sizeof(arr));     getchar(); }

Output 4 3
sizeof(arr) returns the amount of memory used by all elements in array
and sizeof(p) returns the amount of memory used by the pointer variable itself.

Question 4

int x = 0; int f() {    return x; }   int g() {    int x = 1;    return f(); }   int main() {   printf("%d", g());   printf("\n");   getchar(); }

Output: 0
In C, variables are always statically (or lexically) scoped. Binding of x inside f() to global variable x is defined at compile time and not dependent on who is calling it. Hence, output for the above program will be 0.

On a side note, Perl supports both dynamic ans static scoping. Perl’s keyword “my” defines a statically scoped local variable, while the keyword “local” defines dynamically scoped local variable. So in Perl, similar (see below) program will print 1.

$x = 0; sub f {    return $x; } sub g {    local $x = 1; return f(); } print g()."\n";

Reference:
http://en.wikipedia.org/wiki/Scope_%28programming%29

Please write comments if you find any of the above answers/explanations incorrect.