Rewriting nested for loop as a single for loop without redundancy in C for OpenMP

Question

I am trying to make a function that, in a list of arrays, will compare each array to every array that comes after it: Array 0 will compare itself to Arrays 1, 2, 3, 4 and so on, Array 1 will compare itself to Arrays 2, 3, 4 and so on, but not 0, as we already compared it. The same goes for the rest: Array 2 will compare itself to 3, 4 and so forth.

Normally this could be done with a simple nested for loop:

for (int i = 0; i <= number_of_arrays - 1; i++){
    for (int j = i+1; j<= number_of_arrays; j++){
        printf("Comparing Array %d with Array %d", i, j);
    }
}

However, since i'm using OpenMP, i can't use a #pragma omp for inside another. The solution would usually be using collapse(2) as well, but i also can't use since the counter of my internal loop is dependant of the counter of my external one.

In order to not have this problem, i must turn this into a single for loop, the general solution to this seem to be:

for (int i = 0; i <= (number_of_arrays - 1)*number_of_arrays; i++){
       printf("Comparing Array %d with Array %d", i/number_of_arrays, i%number_of_arrays);
   }
}

This, however, will cause redundancy of my code, as i will, for instance, compare Array 0 to Array 1, and later Array 1 to Array 0. How can i turn what i have into a single for loop that will not do redundant comparisons?

Answer 1

for (int i = 0; i <= (number_of_arrays - 1)*number_of_arrays; i++)
{
    if(i%number_of_arrays > i/number_of_arrays)
       printf("Comparing Array %d with Array %d\n", i/number_of_arrays, i%number_of_arrays);
}