Question

I need the set the elements of a very large array in a loop. The loop may continue in certain cases, so the array position must be counted separately.

I always need to set 10 consecutive elements. (10 is an example. In some scenarios, I might need 30 or more.)

Is k+c (c=0,1,2,… constant) or k++ a better approach? Which is more efficient from the two solutions below, and why?

int k = 0;
for (int i = 0; i < aVeryHighNumber; i++) {                 
    if (continueRequired()) {
        continue;
    }

    k = ... // get k as a result of a certain calculation

    veryLargeArray[k++] = value0; // these values might be calculated on-the-fly
    veryLargeArray[k++] = value1;
    veryLargeArray[k++] = value2;
    veryLargeArray[k++] = value5;
    veryLargeArray[k++] = value4;
    veryLargeArray[k++] = value5;
    veryLargeArray[k++] = value6;
    veryLargeArray[k++] = value4;
    veryLargeArray[k++] = value7;
    veryLargeArray[k++] = value1;                   
}

The second solution:

for (int i = 0; i < aVeryHighNumber; i++) {                 
    if (continueRequired()) {
        continue;
    }

    k = ... // get k as a result of a certain calculation

    veryLargeArray[k]      = value0;
    veryLargeArray[k + 1]  = value1;
    veryLargeArray[k + 2]  = value2;
    veryLargeArray[k + 3]  = value5;
    veryLargeArray[k + 4]  = value4;
    veryLargeArray[k + 5]  = value5;
    veryLargeArray[k + 6]  = value6;
    veryLargeArray[k + 7]  = value4;
    veryLargeArray[k + 8]  = value7;
    veryLargeArray[k + 9]  = value1;
}

In theory, the second solution performs 9 add operations (it’s basically an unrolled loop), while the first one does 9 incrementing, i.e. it needs to store the value of k as well. However, self-incrementing by one is probably a very efficient operation nowadays, so I’m not sure if the second solution is faster or not.

Answer 1

As far as the compiled code is represented it is simply binary additions.
The ++ code is simply short hand for +1. When these are converted to binary additions after compiling there is no difference between the two.

Even if there does happen to be a difference any modern computer would show no difference in computation times until you do this 1000’s of times.