[Macluawn]

True, although for small values you won`t have a problem.
But if you must..if you know the maximum level before hand, DP can be used (dynamic programming)

pawn Код:

levelPoints(level)
{
    new points[100];
    points[0] = 0;
    for(new i=1; i <= level; ++i) {
        points[i] = points[i-1] + 10*i;
    }

    return points[level];
}

EDIT:
In this case the array isn`t even needed.

pawn Код:

levelPoints(level)
{
    new points = 0;
    for(new i=1; i <= level; ++i) {
        points += 10*i;
    }

    return points;
}