Array index syntax question

I found this way of resolving array indexes in a code base. Does anyone know how this is able to resolve this define to the appropriate array index?

Code:

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#include <stdio.h>
#include <stdlib.h>


#define PARAMS1 1,1,0
#define PARAMS2 1,1,2


int main()
{
    u_int16_t temp[4] = {0};
   
    temp[1,1,0 / 2] = 5;
    temp[1,1,2 / 2] = 6;


    printf("temp1 index %d\n", (1,1,0)/2); // resolves to index 0
    printf("temp2 index %d\n", (1,1,2)/2); // resolves to index 1
   
    for(int i = 0; i < sizeof(temp)/(sizeof(u_int16_t)); i++)
    {
        printf("temp[%d] = %d\n", i, temp[i]);
    }


    return 0;
}

Output:

temp1 index 0
temp2 index 1
temp[0] = 5
temp[1] = 6
temp[2] = 0
temp[3] = 0

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Edit:

It looks like this syntax returns the last value in the list. If anyone can add additional background on what the compiler does with this syntax it would be much appreciated!

Quote:

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Originally Posted by ChipS

It looks like this syntax returns the last value in the list.

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Correct. This is how the comma operator works.
Comma operator - Wikipedia

Quote:

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[...] the comma operator [...] is a binary operator that evaluates its first operand and discards the result, and then evaluates the second operand and returns this value (and type) [...]

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