The provided C program defines a struct S with one member i, a function fun that takes a struct S as an argument and decrements its i member, and a main function that creates a struct S, calls fun with it, and then prints the value of i from the struct.
Let's go through the main points of the program:
1.struct S str1 = { 2 }; initializes a struct S with i set to 2.
2.fun(str1); is called with str1 as an argument. However, since str1 is passed by val-ue, a copy of str1 is made for the function. The fun function then decrements i within its own copy of str1, and this decrement does not affect the original str1 in main.
3.k = str1.i; assigns the value of str1.i (which remains 2 because fun operated on a copy) to k.
4.printf("%d",k); prints the value of k, which is 2.
Given this, the correct answer is:
D. The program outputs 2.
