Question

Could anyone please tell me how “hello” is being printed here? As far as my knowledge goes, local variables are uninitialized. Therefore, I thought the else part should be printed but it’s happening otherwise. Please help.

struct buss{ 
int a;
char b;
};


void main(){

struct buss *p;

if(p==NULL) printf("hello");

else printf("hi");

}

Answer 1

You didn’t initialize p object. Its value is indeterminate.

Reading an uninitialized object is undefined behavior. Undefined behavior means anything can happen. Anything means your program can also crash or print "nose demons".

EDIT: as requested in the comments, to the question “is reading an uninitialized object always undefined behavior?”: for C90, see 3.16 in the definition of undefined behavior, for C11, see 6.3.2.1p2 and for C99, see the C Committee answer in DR#338.