I'm just doing a tutorial on insertion sorting in C, and I'm struggling to understand the way the ! operator is used as the condition for a do while loop.
The condition is just while (!done) but I don't understand how it knows what is not supposed to be equal to the variable done. Something like while (done==0) would make more sense to me.
I'm only just starting to code so sorry if the answer is really obvious! I tried googling it but I found it hard to express the problem...
The code is as follows:
void insertionSortArray (int arr[])
{
for(int i = 1; i < SIZE; i++)
{
int value = arr[i];
int j = i -1;
int done = 0;
do
{
if (arr[j]>value)
{
arr [j+1] = arr[j];
j - -;
if (j<0)
done = 1;
}
else
done = 1;
} while (!done);
arr [j+1] = value;
}
}
Thanks!!
They're exactly the same thing. !done and done == 0 are interchangeable. The thing about C is: it didn't have a "true" boolean type for a long time. Booleans were only introduced in C99.
All zero values are considered false, other values are true. that's why !done is true, for as long as done == 0 (done is 0 -> false, !false -> true). ! is the logical NOT operator, as always, and does what it does: negates whatever comes after. Therefore done = 0 => done is false, !done -> the opposite of false, being true.
If you find done == 0 easier to read, then by all means write it like that. Although, it is more common to see the shorter version.
False/true checks that are Very common:
type *foo = malloc(123 * sizeof *foo);
if (!foo)
exit(1); // failed to alloc memory
void my_function(int *ptr, size_t size)
{
if (!ptr)
return; // a NULL pointer was passed
// ...
}
Because both statements are interchangeable, write what you find makes the most sense. Perhaps reading both statements aloud (although it may seem silly) will make you change your mind:
while done equals zero
//vs
while not done
Which of the two sentences makes most sense now?