CODEWITHSUNDEEP
c++
user2880990
user2880990

Reputation: 29

What's the difference between these two conditions?

The expression j > 0 && a[j - 1] > value_to_insert appears in the definition of the sort_ints function. Why would it not be acceptable to rewrite this as a[j-1] > value_to_insert && j > 0? I tried putting the condition the other way around and it gave me the same output as the original.

Here's the function definition:

void sort_ints(int *a, int n)
{
    int i;
    int j;
    int value_to_insert;

    for (i = 1; i < n; i++) {
        value_to_insert = a[i];

        /* Shift values greater than value_to_insert. */
        j = i;
        while (j > 0 && a[j - 1] > value_to_insert) {
            a[j] = a[j - 1];
            j--;
        }
        a[j] = value_to_insert;
    }
}

Upvotes: 1

Views: 91

Answers (2)

user529758
user529758

Reputation:

Because due to the short-circuiting property of the && operator, the modified code (your "working" version, that doesn't really work) would most likely invoke undefined behavior by accessing the -1th element in the array.

Upvotes: 3

Kerrek SB
Kerrek SB

Reputation: 477040

It's undefined behaviour to evaluate a[-1]. Since the logical-AND operator && has short-circuited semantics, a[j - 1] is never evaluated if j == 0 in the original code.

Upvotes: 1

Related Questions