consider the program:

Question

Answer 1

str = "Gate2015";

In memory

1000: G
1001: a
....
1007: 5
1008: \0

Now, str has the value 1000.
In the function, while loop terminates when P1 points to '\0' (which has integer value 0). So, P1 = 1008. And P1-P2 returns (1008-1000)/1 = 8 as size of char is 1 in C.

Answer 2

I think size of the string will be printed .... see we pass the base address of the string to madeeasy .... we store it into an initial pointer than we do while statement to find null, we increment address in between this than finally we subtract the base address with this incremented address and return.

Comments

how does  while(0);  work?

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it is null '\0' at last

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its strlen actually (but won't work for null string). sizeof also counts the '\0';