pre Decrement vs. post Decrement

When should I use pre decrement and when to use post decrement?

and for the following code snippet, should I use pre or post decrement.

static private void function(int number)
{
    charArr = new char[number];
    int i = 0;
    int tempCounter;
    int j = 0;
    while(charrArr!=someCharArr)
    {
        tempCounter = number - 1;
        password[tempCounter] = element[i%element.Length];
        i++;
        //This is the loop the I want to use the decrementing in.
        //Suppose I have a char array of size 5, the last element of index 5 is updated
        //in the previous statement.
        //About the upcoming indexes 4, 3, 2, 1 and ZERO.
        //How should I implement it?
        // --tempCounter or tempCounter-- ?
        while (charArr[--tempCounter] == element[element.Length - 1])
        {
        }
    }
}

sikas

출처 c# decrement

As far as your code goes, I guess that it should be tempCounter = number;, password[tempCounter - 1] and charArr[--tempCounter] despite the fact that the while-loop will work on a non-initialized array and tempCounter can become negative. - sjngm
Possible duplicate of What is the difference between ++i and i++ - TylerH

2 답변

You use pre-decrement if you want to decrement the variable before the value is passed on to the remaining expression. On the other hand, a post-decrement evaluates the expression before the variable is decremented:

int i = 100, x;
x = --i;                // both are 99

and

int i = 100, x;
x = i--;                // x = 100, i = 99

The same obviously is true for increments.

so charArr[--tempCounter] will differ in the value from charArr[tempCounter--] in the condition of the while loop. This will decrement the tempCounter before checking the condition. - sikas
@sikas: I don't understand your second line. Both versions will cause the same value to be used inside the loop. The pre/post-decrement only affects what's happening inside the while-expression. - sjngm

you should have ++i; (not that it matters), and should have tempCounter-- Otherwise you will miss the "first" index of charArr

In C#, iirc, pre- vs. post-increment/decrement make no difference in speed. - Jeff Hubbard
I`m updating the values of the charArr in the second while loop from the last index - 1 till index = ZERO. so in the condition of the loop should I use tempCounter-- or --tempCounter? - sikas
This may be true for built in times, but is generally untrue for user classes that define these operators. --i; may be faster, but is never slower than i--;. But we both know a line like i--; will be compiler optimized especially when i is of type int. - EnabrenTane
@sikas I would use while(tempCounter > 0) { charArr[tempCounter--] = /* value */ } - EnabrenTane

pre Decrement vs. post Decrement

2 답변

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