// y = y + t;
// i++; j+=2;
multiply (p, p, i);
divide (p, p, j);
multiply (t, t, i);
add (t, t, p);
divide (t, t, j);
add (y, y, t);
i++;
j += 2;
}
}

Here is the output of the program:

Calculating Catalan's constant to 300000 decimals

Time required: 1 day 8 hour 15 min 15 sec 55 hsec
--------------------------------------------------------------------------
additional REFERENCES :

Catalan constant is : sum((-1)**(n+1)/(2*n-1)**2,n=1..infinity) also known
under the name beta(2), see ?catalan in Maple for more details.

The previous record was 200000 digits, also from Thomas Papanikolaou
and before that : 100000 digits
was due to Greg Fee and Simon Plouffe on August 14, 1996,
by using a SGI r10000 Power Challenge with 194 Mhz in 5.63 hours
and the standard implementation of Catalan on MapleV, Release 4.
(which uses Greg's idea).