class CountWheat {
public static void main (String args[]) {
int i, j, k;
j = 1;
k = 0;
for (i=1; i <= 64; i++) {
k += j;
j *= 2;
System.out.print(k + "\t ");
if (i%4 == 0) System.out.println();
}
System.out.println("All done!");
}
}
% javac CountWheat.java % java CountWheat 1 3 7 15 31 63 127 255 511 1023 2047 4095 8191 16383 32767 65535 131071 262143 524287 1048575 2097151 4194303 8388607 16777215 33554431 67108863 134217727 268435455 536870911 1073741823 2147483647 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 All done! %What happened? After 2,147,483,647 grains of wheat were counted the next number should have been 4,294,967,295. However an int can't be larger than 2,147,483,647. The number instead wrapped around into the negative numbers and stayed there.
You can improve your results slightly (but only slightly) by changing the ints to longs. A long is an integer type variable that can hold up to 9,223,372,036,854,775,807. However even that isn't quite large enough to count how much wheat the king owed. To accurately calculate the king's debt use a double, the largest type of all.