So I have some code here that I have been studying. It converts decimal numbers to binary. The code runs smoothly but what's bugging me are the variables. The code is as follows:

#include 
int main()
{
    long int decimalNumber, remainder, quotient;
    int binaryNumber[100], i=1, j;

    printf("Enter any decimal number: ");
    scanf("%ld",&decimalNumber);

    quotient = decimalNumber;
    while (quotient!=0) {
        binaryNumber[i++]= quotient % 2;
        quotient = quotient / 2;
    }
    printf("Equivalent binary value of decimal number %d:       ", decimalNumber);

    for (j = i -1 ; j> 0;  j--)
        printf("%d",binaryNumber[j]);

    return 0;
}

I really find the variables confusing. Can someone tell me what is actually happening with the variables? Especially the one with binaryNumber[100],binaryNumber[i++], binaryNumber[j], and the expression binaryNumber[i++] = quotient % 2