function getAssignmentDirection(update, counter) {
			if (update.left.name === counter) {
				if (update.operator === "+=") {
					return getRightDirection(update, 1);
				}
				if (update.operator === "-=") {
					return getRightDirection(update, -1);
				}
			}
			return 0;
		}
check AssignmentExpression add/sub the counter
@param {ASTNode} update AssignmentExpression to check
@param {string} counter variable name to check
@returns {number} if add return 1, if sub return -1, if nochange, return 0