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c#arraysfor-loopincrement

For-loops, array and ++ operator

Beginner asking a question.

I am testing the increment ++ operator within for-loop and the outcome is different than I expect it to be and I have no clue why. The code is not for a specific program.

        int[] numbers = new int[10];

        for (int i = 0; i < 10; i++)
        {
            numbers[i] = i++;
        }

        for (int a = 0; a < 10; a++)
        {
            Console.WriteLine("value is {0} at position {1}", numbers[a], a);
        }

Output is:

value is 0 at position 0
value is 0 at position 1
value is 2 at position 2
value is 0 at position 3
value is 4 at position 4
value is 0 at position 5
value is 6 at position 6
value is 0 at position 7
value is 8 at position 8
value is 0 at position 9

If i run the first for-loop without the ++ increment (numbers[i] = i;), the values are consecutive and in order (0, 1, 2, 3 etc.). Why the ++ increment causes every other value to be zero? I thought it would be something like 0, 2, 4, 6, 8, 10 etc.

If I run numbers[i] = i+1; outcome is something I would expect:

value is 1 at position 0
value is 2 at position 1
value is 3 at position 2
value is 4 at position 3
value is 5 at position 4
value is 6 at position 5
value is 7 at position 6
value is 8 at position 7
value is 9 at position 8
value is 10 at position 9
Solution

  • The code you write is

    for (int i = 0; i < 10; i++)
{
    numbers[i] = i++;
}

    that is equal to

    for (int i = 0; i < 10; i++)
{
    numbers1[i] = i;
    i = i + 1;
}

    First time i is start from 0

    // I change the i to real value for easy understanding
for (int i = 0; i < 10; i++)
{
    numbers1[0] = 0;
    i = 0 + 1;
    //so here i is 1
}

    Second time i is 2, because after first time loop the i is 1 then the for (int i = 0; i < 10; i++) will increase i from 1 to 2, so the second time loop will be

    for (int i = 0; i < 10; i++)
{
    numbers1[2] = 2;
    i = 2 + 1;
    //so here i is 3
}

    So now you know the numbers[0] is 0 and numbers[2] is 2 but about the numbers[1] you don't set the value for it so it will be the default value which the default value of int is 0.