Fun exam questions

Some of you may know I've been a C programming tutor for a few years.

If you're taking a C programming course at university these are some of the harder types of questions you might find on a final exam:

Q1: Is the following valid C?

Q2: How many times does the following code print "hello\n"?

Q3: What does the following code do?

Q4: Why is the following a bad idea?

Q5: What would the following code do?

Q6: What is the following code equivalent to?

Q7: What is the type of foo in the following? Is it valid C?

Q8: what is the return value of this function?

Q9: What is the value of c after the following code is executed (assuming c is 2 before execution)?:

 

Correct, it is deferencing the address 'z' (the asciicode of z) and assigning it the value '010', which is octal for 8. The branch would always be taken because it is an assignment and an not equality operator; But in this case the if-statement is followed immediately by a semicolon, so the following statement is not part of any branch -- it is instead an independent code-block.

You should take in an order of precedence table of operators if you are allowed. This might help you solve a question like 9.

In this particular case I believe the language states the code is ambiguous and undefined.

One might interpret it as:
c += (c++) + (+c); // or
c += (c) + (+(++c));

 

Wrong.

Wrong. Look up #define macros.

Wrong.

Wrong.

Wrong/Didn't answer the question.

Wrong.

Wrong/Didn't answer the question.

Wrong.

Wrong.

You scored: 0/9.

 

int main() {

// define a pointer (called main) to a function that takes unknown arguments and returns an int.
int (*main)();

{ // free standing codeblock.

printf("hello world\n");

return 0;
​

}
​

}

 

Correct.

Correct.

Wrong/Didn't answer.

int main(void); //Prototype for main
int(*__)()=main; // Function pointer called __ which points at main
int(**_)()=&__; // Function pointer pointer called _ which points at __
int main(void){
(*_)(); // dereference _, and call the resulting function pointer. (Infinite recursion.)
}

Correct, fork bomb.

Half mark, didn't answer the question but got halfway there.

(It is intentional, and it's good you picked it up.)

The code dereferences the ascii-code for 'z' and sets the memory there to octal 010. (decimal 8). It then proceeds to the unconnected codeblock, and prints the memory at the address which is the ascii-code of 'z', which we just set to 010, which is 8. So it prints 8.

Wrong/didn't answer the question.

The code is equivalent to the following:
char a[10];
int b = 5;
a = 5;

or

char a[10];
a[5] = 5;

Wrong, it's a function pointer. I won't reveal what type of function pointer.

Wrong.

The last value or variable in a code-block is it's value if used in an expression. This is actually valid C but not all compilers support it. That function returns the octal value 011.

It's ambiguous, it depends on the compiler. I'll give you this mark.

Your score: 4.5/9.

 

Any respectable computer science or IT degree will contain at minimum one course in each C and Java programming. You might also get your hands on C++ depending on how good the university is.