Dunno! But what about some formatting twist to make it harder:  

Reformatted:

1. void setup() {
2.   int[] a = new int[10];
3.   int i=1, c=1;
4.  
5.   while (i<a.length) {
6.     if (c%4==0) {
7.       a[i]=c-a[i-1];
8.       i++;
9.     }
10.  
11.     c++;
12.   }
13.  
14. println(a);
15. /*
16.   for (int j=0;j<a.length-1;j++)
17.     print(a[j]+",");
18.   print(a[i-1]+".");
19. */
20. }

Output:
[0] 0
[1] 4
[2] 4
[3] 8
[4] 8
[5] 12
[6] 12
[7] 16
[8] 16
[9] 20

Not sure if that's the expected result or what interest it has.

 int[] a = new int[10]; 

make an array of integers and call it "a" and give it 10 pigeonholes

int i=1,c=1; 

make two integers i and c and set them equal to 1

while(i<a.length)

while i < length of the array a, so less than 10

{ 

if(c%4==0)

if c modulo 4 is 0, or if c is an integer multiple of 4 (4, 8, 12 ...)

{

 a[i] = c - a[i-1];

make the ith entry of the array a equal to c - (i-1)th entry in the array a 

i++; }

 c++;

add 1 to i and add 1 to c

 }

 for(int j=0;j<a.length-1;j++)

for j equaling the values 0, 1, 2, ... 9 in turn

print(a[j]+","); 

print(a[i-1]+"."); 

print these things: the jth value in the array a and the (i-1)th value in the array a

}

gotoloop's joking aside, it's appallingly formated

void setup()
{
 int[] a = new int[10];
 int i = 1;
 int c = 1; 

while(i < a.length)
{ 
 if(c % 4 = =0)
 {
   a[i] = c - a[i - 1];
   i++; 
 }
 c++;
 }
 for(int j = 0; j < a.length - 1; j++) 
{
  print(a[j] + ","); 
  print(a[i - 1] + "."); 
}
}