C Programming Final Exams

Kassem · 2010-06-18T10:37:52+00:00

Hey guys, I've got my final exam coming up this Monday. I got the final exams of the last couple of years from my faculty's print-press. I thought I'd share...

rolf

arithma wroteIf I had to choose a trainee who knew how to program and think in comparison to one who knew standards and was anal about it I'd be happy to pick the one who knew how to think.

Anal is hot!

Kassem

Padre wrote1- Integer
2- There are numerous ways to pass arrays to a function, this is one of them :D
3-Nop, only diagonal. a single loop from 1 till size, and im always taking item 1,1 - 2,2 - 3,3 -> diagonal.

1. oh I see... I thought '%d' is for integer...
2. Mind mentioning some of the others? :D
3. Oh yeah you're right... But you're missing the other diagonal though... and that can be considered using A[ARY_SIZE - i][ARY_SIZE - i]

Anyway, thanks for the help man. Appreciated :)

rolf

nuclearcat wrote1.

int func (int *array,int length) {
    int i;
    for (i=0;i<(length/2);i++) {
       array[i] ^= array[length-1-i];
       array[length-1-i] ^= array[i];
       array[i] ^= array[length-1-i];
    }
}

Code is not portable. There is few other tricky ways possible...

That's some crazy code you got there!
Why not just create a new array and fill it backwards?
I know, your code is probably faster, but what difference does it make in this case?
In any case?? Unless you're programming critical kernel functions, in most cases it wont matter.

arithma

rolf wrote
arithma wroteIf I had to choose a trainee who knew how to program and think in comparison to one who knew standards and was anal about it I'd be happy to pick the one who knew how to think.
Anal is hot!

Maybe skirt anal. Even then..

Kassem, you still need anything?

Kassem

arithma wroteKassem, you still need anything?

I just need to understand how to pass an array as an argument of a function. My prof. said the function should be expecting a pointer, but Padre's code doesn't show that...

arithma

void print_ary(int* A, int rows, int columns)
{
    int i;
    int j;
    for (i=0;i<rows;i++)
    {
        for (j=0;j<columns;j++)
            printf("%i \t",A[i*rows+j]);
         printf("\n");
    }
}

This code will allow you to access 2D arrays of arbitrary width and height. The thing to note is that internally, A[1][0] comes right after A[0][columns-1], that's why we can use index multiplication.

You'd pass in print_ary(&A[0][0], ARY_SIZE, ARY_SIZE)..

Enjoy :)

Padre

or if you want to keep the A[X][Y] u can use

 print_ary(int **A, int rows, int columns)

if i remember correctly

rolf

@nuclearcat, you have a problem in your code,
I think the 3rd line:

       array[i] ^= array[length-1-i];

Is a mistake, and it's the same then the 1st one.

It's f*** crazy though, bitwise XOR can actually reverse the array :)
I did it with a paper and a pen, and it works! Took me 1/2 hour to understand.

arithma

Padre wroteor if you want to keep the A[X][Y] u can use

 print_ary(int **A, int rows, int columns)

if i remember correctly

You can't since it has no way to know what size the dimension is (int ** can mean any dimension). What you probably meant was:
int (*A)[ARY_SIZE] is the closest thing you'll get.
You can use the A[j] with this declaration, and to pass arguments in as well.

arithma

You guys should take the program apart, and implement swap apart from the array reversal to make things clear.

nuclearcat

rolf wrote@nuclearcat, you have a problem in your code,
I think the 3rd line:
       array[i] ^= array[length-1-i];
Is a mistake, and it's the same then the 1st one.

It's f*** crazy though, bitwise XOR can actually reverse the array :)
I did it with a paper and a pen, and it works! Took me 1/2 hour to understand.

From wiki

Conventional swapping requires the use of a temporary storage variable. Using the XOR swap algorithm, however, no temporary storage is needed. The algorithm is as follows:

X := X XOR Y
Y := X XOR Y
X := X XOR Y

length-1-i is also correct, so when i have index value 0, i will use to swap it with last element (since count is from 0, then it is length-i-1

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