Prog\ What is the output

Question

#include <stdio.h>
#define crypt(s,t,u,m,p,e,d) m##s##u##t
#define begin crypt(a,n,i,m,a,t,e)
int begin()
{
    printf("Hello\n");
    return 0;
}

---

Options are :

(a) Hello (b) Link error (c) Segmentation fault (d) Compiler error

Comments

Explanation please.

Answer 1

Answer A  Hello

Let us analyse the code:

1. #include <stdio.h>
2. #define crypt(s,t,u,m,p,e,d) m##s##u##t
3. #define begin crypt(a,n,i,m,a,t,e)
4. int begin()
5. {
6.     printf("Hello\n");
7.     return 0;
8. }

Line 1 : includes stdio.h 

Line 2: defined a macro crypt. It accepts 7 characters are makes a string with fourth, first, third and second letters and replaces the macro call with the result string. eg: crypt(b,d,c,a,e,f) replaces with abcd

Line 3: says that wherever string begin occurs, compiler should replace it with crypt(a,n,i,m,a,t,e) ie string main

Line 4: compiler sees begin here. Immediately it replaces begin with the string main (See point 3)

Now line 4 becomes int main()

Compiler detects a main programs. Thus function begin() is equivalent to main () program

hence "Hello" is printed.